Re: [racket-users] Re: nested for loops and suggested alternatives

[Daniel Prager]

Hi Travis

Glad you found it instructive.

In mathematical terms these kinds of systems map from the current state at
t=n to the next time-step at t=n+1.

Given a transition function I tend to just use for/list (or for/vector) to
build up a history.

E.g.

#lang racket

(require math/matrix)

(define A (matrix [[0 0 5.905]
   [0.368 0.639 0.025]
   [0.001 0.152 0.051]]))

(define n (col-matrix [5 5 5]))

(define (iterate A n iter)
  (for/list ([i iter])
(define temp n)
(set! n (matrix* A n))
(list i temp)))

(iterate A n 25)


You could use for/fold, which avoids the use of set!, but the syntax is a
little heavier.

Dan

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Re: [racket-users] Re: nested for loops and suggested alternatives

[travis . hinkelman]

For the benefit of other beginners, I think there was a small typo in 
prop-projection.v1 where the intention was to call that function 
recursively rather than calling pop-projection in the body of 
pop-projection.v1. The typo is corrected below:

(define (pop-projection.v1 A n iter)
  (if (zero? iter)
  (list n)
  (cons n (pop-projection.v1 A (matrix* A n) (- iter 1)

Thanks to everyone for the feedback. It has been very illuminating!



On Sunday, February 10, 2019 at 5:49:01 PM UTC-8, Matthias Felleisen wrote:
>
>
>
> On Feb 10, 2019, at 7:26 PM, Alex Harsanyi  > wrote:
>
> One way to do this is for `pop-abundances` to have an extra parameter, the 
> list of previous abundances, and whenever the function is called 
> recursively, it adds the current abundance to this list and passes it on to 
> the next call.  The final call will than return this result instead of the 
> last abundance.  In the example below, "cons" adds to the front of the 
> list, so "result" contains the most recent values first and  this list is 
> reversed before being returned to the user.  Also, when `pop-abundances` is 
> invoked by the user, there are no "previous abundances" , so it needs to be 
> invoked with an empty list -- this is handled by a default parameter for 
> 'result':
>
> #lang racket
> (require math/matrix)
>
> (define A (matrix [[0 0 5.905]
>[0.368 0.639 0.025]
>[0.001 0.152 0.051]]))
>
> (define n (col-matrix [5 5 5]))
>
> (define (pop-projection A n iter [result '()])
>   (if (zero? iter)
>   (reverse (cons n result))
>   (pop-projection A (matrix* A n) (- iter 1) (cons n result
>
> (pop-projection A n 25)
>
>
>
>
> Don’t use accumulators if the function has all the information: 
>
> #lang racket
>
> (require math/matrix)
>
> (define A
>   (matrix
>[[0 0 5.905]
> [0.368 0.639 0.025]
> [0.001 0.152 0.051]]))
>
> (define n (col-matrix [5 5 5]))
>
> (define (pop-projection A n iter [result '()])
>   (if (zero? iter)
>   (reverse (cons n result))
>   (pop-projection A (matrix* A n) (- iter 1) (cons n result
>
> (define (pop-projection.v1 A n iter)
>   (if (zero? iter)
>   (list n)
>   (cons n (pop-projection A (matrix* A n) (- iter 1)
>
> (equal? (pop-projection A n 25) (pop-projection.v1 A n 25))
>
>

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Re: [racket-users] Re: nested for loops and suggested alternatives

[Matthias Felleisen]

> On Feb 10, 2019, at 7:26 PM, Alex Harsanyi  wrote:
> 
> One way to do this is for `pop-abundances` to have an extra parameter, the 
> list of previous abundances, and whenever the function is called recursively, 
> it adds the current abundance to this list and passes it on to the next call. 
>  The final call will than return this result instead of the last abundance.  
> In the example below, "cons" adds to the front of the list, so "result" 
> contains the most recent values first and  this list is reversed before being 
> returned to the user.  Also, when `pop-abundances` is invoked by the user, 
> there are no "previous abundances" , so it needs to be invoked with an empty 
> list -- this is handled by a default parameter for 'result':
> 
> #lang racket
> (require math/matrix)
> 
> (define A (matrix [[0 0 5.905]
>[0.368 0.639 0.025]
>[0.001 0.152 0.051]]))
> 
> (define n (col-matrix [5 5 5]))
> 
> (define (pop-projection A n iter [result '()])
>   (if (zero? iter)
>   (reverse (cons n result))
>   (pop-projection A (matrix* A n) (- iter 1) (cons n result
> 
> (pop-projection A n 25)
> 



Don’t use accumulators if the function has all the information: 

#lang racket

(require math/matrix)

(define A
  (matrix
   [[0 0 5.905]
[0.368 0.639 0.025]
[0.001 0.152 0.051]]))

(define n (col-matrix [5 5 5]))

(define (pop-projection A n iter [result '()])
  (if (zero? iter)
  (reverse (cons n result))
  (pop-projection A (matrix* A n) (- iter 1) (cons n result

(define (pop-projection.v1 A n iter)
  (if (zero? iter)
  (list n)
  (cons n (pop-projection A (matrix* A n) (- iter 1)

(equal? (pop-projection A n 25) (pop-projection.v1 A n 25))

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Re: [racket-users] Re: nested for loops and suggested alternatives

[Alex Harsanyi]

On Monday, February 11, 2019 at 8:01:47 AM UTC+8, travis.h...@gmail.com 
wrote:
>
> Thanks, Daniel, this is helpful. I think that I understand your code, but 
> it is a still a foreign way of thinking for me. Of course, that is a big 
> part of why I'm learning Racket, i.e., to make programming with lists and 
> recursion more natural. One key gap for me is how to build up data 
> structures using lists and recursion. Perhaps the answer is that you don't 
> build up the data structure in memory but by writing to disk. In this 
> particular example, it is useful to have the values at every iteration for 
> plotting the population trajectory (by age class or summed across age 
> classes). 
>
> Below is a little example I was exploring that involves matrix 
> multiplication (col-matrix is abundance in different age classes; square 
> matrix is transition probabilities among age classes). It was obvious to me 
> how to use recursion to get the final col-matrix of abundances but not how 
> to build up a data structure that included the abundances at every 
> iteration.
>

One way to do this is for `pop-abundances` to have an extra parameter, the 
list of previous abundances, and whenever the function is called 
recursively, it adds the current abundance to this list and passes it on to 
the next call.  The final call will than return this result instead of the 
last abundance.  In the example below, "cons" adds to the front of the 
list, so "result" contains the most recent values first and  this list is 
reversed before being returned to the user.  Also, when `pop-abundances` is 
invoked by the user, there are no "previous abundances" , so it needs to be 
invoked with an empty list -- this is handled by a default parameter for 
'result':

#lang racket
(require math/matrix)

(define A (matrix [[0 0 5.905]
   [0.368 0.639 0.025]
   [0.001 0.152 0.051]]))

(define n (col-matrix [5 5 5]))

(define (pop-projection A n iter [result '()])
  (if (zero? iter)
  (reverse (cons n result))
  (pop-projection A (matrix* A n) (- iter 1) (cons n result

(pop-projection A n 25)


Alex. 


> (require math/matrix)
>
> (define A (matrix [[0 0 5.905]
>[0.368 0.639 0.025]
>[0.001 0.152 0.051]]))
>
> (define n (col-matrix [5 5 5]))
>
> (define (pop-projection A n iter)
>   (if (zero? iter) n
>   (pop-projection A (matrix* A n) (- iter 1
>
> (pop-projection A n 25)
>
>
>
> On Sunday, February 10, 2019 at 3:56:25 AM UTC-8, Daniel Prager wrote:
>>
>> Thanks for the screenshot Travis.
>>
>> Just for fun, here's a version in Racket that eschews assignment, vectors 
>> and for loops, in favour of recursion and lists ...
>>
>> #lang racket
>>
>> (define years 30)
>> (define prop-female 0.5)
>> (define egg-surv 0.6)
>>
>> (define fecundity '(0 0 200 400 800))
>> (define survival '(0.2 0.4 0.6 0.8 0))
>> (define capacity '(1e6 1e5 1e4 1e3 1e2 -))
>> (define cap0 (first capacity))
>>
>> (define (beverton-holt N p c) (/ N (+ (/ 1 p) (/ N c
>>
>> (define (evolve N [f fecundity] [s survival] [cap (rest capacity)] [Nt0 
>> 0] [Nt null])
>> (if (null? f)
>> (cons Nt0 (reverse Nt))
>> (evolve (rest N) (rest f) (rest s) (rest cap)
>> (+ Nt0 (if (= (first f) 0)
>>0
>>(beverton-holt (* (first N) prop-female)
>>   (* (first f) egg-surv)
>>   (- cap0 Nt0
>> (if (= (first s) 0)
>> Nt
>> (cons (beverton-holt (first N) (first s) (first cap)) 
>> Nt)
>>
>> (define (iterate N n [i 1])
>>   (displayln (list i N))
>>   (unless (= i n) (iterate (evolve N) n (+ i 1
>>
>> (iterate (make-list (length fecundity) 10) years)
>>
>

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Re: [racket-users] Re: nested for loops and suggested alternatives

[travis . hinkelman]

Thanks, Daniel, this is helpful. I think that I understand your code, but 
it is a still a foreign way of thinking for me. Of course, that is a big 
part of why I'm learning Racket, i.e., to make programming with lists and 
recursion more natural. One key gap for me is how to build up data 
structures using lists and recursion. Perhaps the answer is that you don't 
build up the data structure in memory but by writing to disk. In this 
particular example, it is useful to have the values at every iteration for 
plotting the population trajectory (by age class or summed across age 
classes). 

Below is a little example I was exploring that involves matrix 
multiplication (col-matrix is abundance in different age classes; square 
matrix is transition probabilities among age classes). It was obvious to me 
how to use recursion to get the final col-matrix of abundances but not how 
to build up a data structure that included the abundances at every 
iteration.

(require math/matrix)

(define A (matrix [[0 0 5.905]
   [0.368 0.639 0.025]
   [0.001 0.152 0.051]]))

(define n (col-matrix [5 5 5]))

(define (pop-projection A n iter)
  (if (zero? iter) n
  (pop-projection A (matrix* A n) (- iter 1

(pop-projection A n 25)



On Sunday, February 10, 2019 at 3:56:25 AM UTC-8, Daniel Prager wrote:
>
> Thanks for the screenshot Travis.
>
> Just for fun, here's a version in Racket that eschews assignment, vectors 
> and for loops, in favour of recursion and lists ...
>
> #lang racket
>
> (define years 30)
> (define prop-female 0.5)
> (define egg-surv 0.6)
>
> (define fecundity '(0 0 200 400 800))
> (define survival '(0.2 0.4 0.6 0.8 0))
> (define capacity '(1e6 1e5 1e4 1e3 1e2 -))
> (define cap0 (first capacity))
>
> (define (beverton-holt N p c) (/ N (+ (/ 1 p) (/ N c
>
> (define (evolve N [f fecundity] [s survival] [cap (rest capacity)] [Nt0 0] 
> [Nt null])
> (if (null? f)
> (cons Nt0 (reverse Nt))
> (evolve (rest N) (rest f) (rest s) (rest cap)
> (+ Nt0 (if (= (first f) 0)
>0
>(beverton-holt (* (first N) prop-female)
>   (* (first f) egg-surv)
>   (- cap0 Nt0
> (if (= (first s) 0)
> Nt
> (cons (beverton-holt (first N) (first s) (first cap)) 
> Nt)
>
> (define (iterate N n [i 1])
>   (displayln (list i N))
>   (unless (= i n) (iterate (evolve N) n (+ i 1
>
> (iterate (make-list (length fecundity) 10) years)
>

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Re: [racket-users] Re: nested for loops and suggested alternatives

[Laurent]

perhaps more importantly:

-- (build-vector 5 (lambda (_) (make-vector 5 0)))
-- (make-vector 5 (build-vector 5 (lambda (_) 0)))

On Sun, Feb 10, 2019 at 3:16 PM Gustavo Massaccesi 
wrote:

> To understand the problem, it will be useful to understand the difference
> between
>
> -- (make-vector 5 (make-vector 5))
> -- (build-vector 5 (lambda (_) (build-vector 5 (lambda (_) 0
> -- (for/vector ([_ 5]) (for/vector ([_ 5]) 0))
>
> Gustavo
>
> On Sun, Feb 10, 2019 at 7:24 AM  wrote:
>
>> Yes, this was the problem. I now have results that match the output from
>> R. I've updated the gist with your line for the correct way to create a
>> vector of vectors. I will have to spend some more time to understand the
>> make-vector behavior. Perhaps my thinking is too constrained by my R
>> experience where many functions are "vectorized"? I guess the part that was
>> confusing me (and still is) is why make-vector worked as expected (by me)
>> for my inner vector but not my outer vector. Thanks!
>>
>>
>> On Sunday, February 10, 2019 at 12:42:53 AM UTC-8, Alex Harsanyi wrote:
>>>
>>> This line looks suspicious:
>>>
>>>  (define results (make-vector years (make-vector (vector-length
>>> fecundity) 0)))
>>>
>>> The "(make-vector (vector-length fecundity) 0)" expression will create a
>>> single vector, than it creates the outer vector will all elements pointing
>>> to it.  It is not a matrix, but a "column" vector where each element is
>>> referencing the same row vector.  This means that if you update an element
>>> in one of the rows, the same value will "appear" in all other rows. The
>>> only row that is different is the first one which you initialize in the
>>> line:
>>>
>>> (vector-set! results 0 (make-vector (vector-length fecundity) 10))
>>>
>>> What you probably want is a vector of vectors, which can be built like
>>> this
>>>
>>> (define results (for/vector ([index (in-range years)]) (make-vector
>>> (vector-length fecundity) 0)))
>>>
>>> Alex.
>>>
>>>
>>>
>>> On Sunday, February 10, 2019 at 3:40:42 PM UTC+8, travis.h...@gmail.com
>>> wrote:

 Hi All,

 I'm an R programmer that has recently started learning Racket. I
 decided to start by trying to create a simple age-structured population
 model. In R, I would initialize a matrix and use nested for loops to move
 through the elements of the matrix and propagate the population forward
 through time. For my first attempt in Racket (
 https://gist.github.com/hinkelman/3ee6115cdd7f0a4c8f1672b7d8df5c27), I
 used for* to loop through a vector of vectors. The code in that gist
 doesn't quite work. There is apparently something wrong with how I'm using
 vector-set! such that "rows" in my vector of vectors are being updated
 prematurely. I would greatly appreciate it if someone could point out what
 I'm doing wrong there. I'm also interested in suggestions for alternative
 approaches because it seems unlikely that I have written this code in
 idiomatic Racket.

 Thanks,

 Travis

 P.S. If it is helpful, here is a gist (
 https://gist.github.com/hinkelman/d5b8414b0c6383057d7846509a724bbf)
 with the R code that I was trying to write in Racket.

>>> --
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Re: [racket-users] Re: nested for loops and suggested alternatives

[Gustavo Massaccesi]

To understand the problem, it will be useful to understand the difference
between

-- (make-vector 5 (make-vector 5))
-- (build-vector 5 (lambda (_) (build-vector 5 (lambda (_) 0
-- (for/vector ([_ 5]) (for/vector ([_ 5]) 0))

Gustavo

On Sun, Feb 10, 2019 at 7:24 AM  wrote:

> Yes, this was the problem. I now have results that match the output from
> R. I've updated the gist with your line for the correct way to create a
> vector of vectors. I will have to spend some more time to understand the
> make-vector behavior. Perhaps my thinking is too constrained by my R
> experience where many functions are "vectorized"? I guess the part that was
> confusing me (and still is) is why make-vector worked as expected (by me)
> for my inner vector but not my outer vector. Thanks!
>
>
> On Sunday, February 10, 2019 at 12:42:53 AM UTC-8, Alex Harsanyi wrote:
>>
>> This line looks suspicious:
>>
>>  (define results (make-vector years (make-vector (vector-length
>> fecundity) 0)))
>>
>> The "(make-vector (vector-length fecundity) 0)" expression will create a
>> single vector, than it creates the outer vector will all elements pointing
>> to it.  It is not a matrix, but a "column" vector where each element is
>> referencing the same row vector.  This means that if you update an element
>> in one of the rows, the same value will "appear" in all other rows. The
>> only row that is different is the first one which you initialize in the
>> line:
>>
>> (vector-set! results 0 (make-vector (vector-length fecundity) 10))
>>
>> What you probably want is a vector of vectors, which can be built like
>> this
>>
>> (define results (for/vector ([index (in-range years)]) (make-vector
>> (vector-length fecundity) 0)))
>>
>> Alex.
>>
>>
>>
>> On Sunday, February 10, 2019 at 3:40:42 PM UTC+8, travis.h...@gmail.com
>> wrote:
>>>
>>> Hi All,
>>>
>>> I'm an R programmer that has recently started learning Racket. I decided
>>> to start by trying to create a simple age-structured population model. In
>>> R, I would initialize a matrix and use nested for loops to move through the
>>> elements of the matrix and propagate the population forward through time.
>>> For my first attempt in Racket (
>>> https://gist.github.com/hinkelman/3ee6115cdd7f0a4c8f1672b7d8df5c27), I
>>> used for* to loop through a vector of vectors. The code in that gist
>>> doesn't quite work. There is apparently something wrong with how I'm using
>>> vector-set! such that "rows" in my vector of vectors are being updated
>>> prematurely. I would greatly appreciate it if someone could point out what
>>> I'm doing wrong there. I'm also interested in suggestions for alternative
>>> approaches because it seems unlikely that I have written this code in
>>> idiomatic Racket.
>>>
>>> Thanks,
>>>
>>> Travis
>>>
>>> P.S. If it is helpful, here is a gist (
>>> https://gist.github.com/hinkelman/d5b8414b0c6383057d7846509a724bbf)
>>> with the R code that I was trying to write in Racket.
>>>
>> --
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Re: [racket-users] Re: nested for loops and suggested alternatives

[Daniel Prager]

Thanks for the screenshot Travis.

Just for fun, here's a version in Racket that eschews assignment, vectors
and for loops, in favour of recursion and lists ...

#lang racket

(define years 30)
(define prop-female 0.5)
(define egg-surv 0.6)

(define fecundity '(0 0 200 400 800))
(define survival '(0.2 0.4 0.6 0.8 0))
(define capacity '(1e6 1e5 1e4 1e3 1e2 -))
(define cap0 (first capacity))

(define (beverton-holt N p c) (/ N (+ (/ 1 p) (/ N c

(define (evolve N [f fecundity] [s survival] [cap (rest capacity)] [Nt0 0]
[Nt null])
(if (null? f)
(cons Nt0 (reverse Nt))
(evolve (rest N) (rest f) (rest s) (rest cap)
(+ Nt0 (if (= (first f) 0)
   0
   (beverton-holt (* (first N) prop-female)
  (* (first f) egg-surv)
  (- cap0 Nt0
(if (= (first s) 0)
Nt
(cons (beverton-holt (first N) (first s) (first cap))
Nt)

(define (iterate N n [i 1])
  (displayln (list i N))
  (unless (= i n) (iterate (evolve N) n (+ i 1

(iterate (make-list (length fecundity) 10) years)

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Re: [racket-users] Re: nested for loops and suggested alternatives

[Jens Axel Søgaard]

>
> Performance Warning: Indexing the elements of arrays created in untyped
>> Racket is currently 25-50 times slower than doing the same in Typed Racket,
>> due to the overhead of checking higher-order contracts. We are working on
>> it.
>
>
I have no idea how to improve that (the timings are old - perhaps it has
become better already).

/Jens Axel



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Re: [racket-users] Re: nested for loops and suggested alternatives

[travis . hinkelman]

I played around a bit with the math/matrix library. Actually, my first idea 
for a Racket learning project was to rewrite the code in the R popbio 
package (https://cran.r-project.org/web/packages/popbio/popbio.pdf) in 
Racket. But I bailed on that when I saw that eigendecomposition was still 
on the list of unimplemented but useful algorithms for math/matrix.

Performance is not important for this example but this math/array warning 
gave me the impression that perhaps it was not the best place to start for 
me. 

Performance Warning: Indexing the elements of arrays created in untyped 
> Racket is currently 25-50 times slower than doing the same in Typed Racket, 
> due to the overhead of checking higher-order contracts. We are working on 
> it.


I also thought it would be good to stick to racket/base for my early forays 
with Racket but I would not give that same advice to someone learning R 
(i.e., some R packages greatly ease the introduction to R).


On Sunday, February 10, 2019 at 12:47:52 AM UTC-8, Philip McGrath wrote:
>
> You may also want to look into the math/array 
>  and math/matrix 
>  libraries.
> -Philip
>
>
> On Sun, Feb 10, 2019 at 3:42 AM Alex Harsanyi  > wrote:
>
>> This line looks suspicious:
>>
>>  (define results (make-vector years (make-vector (vector-length 
>> fecundity) 0)))
>>
>> The "(make-vector (vector-length fecundity) 0)" expression will create a 
>> single vector, than it creates the outer vector will all elements pointing 
>> to it.  It is not a matrix, but a "column" vector where each element is 
>> referencing the same row vector.  This means that if you update an element 
>> in one of the rows, the same value will "appear" in all other rows. The 
>> only row that is different is the first one which you initialize in the 
>> line:
>>
>> (vector-set! results 0 (make-vector (vector-length fecundity) 10))
>>
>> What you probably want is a vector of vectors, which can be built like 
>> this
>>
>> (define results (for/vector ([index (in-range years)]) (make-vector 
>> (vector-length fecundity) 0)))
>>
>> Alex.
>>
>>
>>
>> On Sunday, February 10, 2019 at 3:40:42 PM UTC+8, travis.h...@gmail.com 
>> wrote:
>>>
>>> Hi All,
>>>
>>> I'm an R programmer that has recently started learning Racket. I decided 
>>> to start by trying to create a simple age-structured population model. In 
>>> R, I would initialize a matrix and use nested for loops to move through the 
>>> elements of the matrix and propagate the population forward through time. 
>>> For my first attempt in Racket (
>>> https://gist.github.com/hinkelman/3ee6115cdd7f0a4c8f1672b7d8df5c27), I 
>>> used for* to loop through a vector of vectors. The code in that gist 
>>> doesn't quite work. There is apparently something wrong with how I'm using 
>>> vector-set! such that "rows" in my vector of vectors are being updated 
>>> prematurely. I would greatly appreciate it if someone could point out what 
>>> I'm doing wrong there. I'm also interested in suggestions for alternative 
>>> approaches because it seems unlikely that I have written this code in 
>>> idiomatic Racket.
>>>
>>> Thanks,
>>>
>>> Travis
>>>
>>> P.S. If it is helpful, here is a gist (
>>> https://gist.github.com/hinkelman/d5b8414b0c6383057d7846509a724bbf) 
>>> with the R code that I was trying to write in Racket.
>>>
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Re: [racket-users] Re: nested for loops and suggested alternatives

[Daniel Prager]

Hi Travis

Would you mind sharing your results from R (and now Racket)?

I'm having a play with the Racket code, and would like to check I'm not
breaking anything as I refactor it.

Dan

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[racket-users] Re: nested for loops and suggested alternatives

[travis . hinkelman]

Yes, this was the problem. I now have results that match the output from R. 
I've updated the gist with your line for the correct way to create a vector 
of vectors. I will have to spend some more time to understand the 
make-vector behavior. Perhaps my thinking is too constrained by my R 
experience where many functions are "vectorized"? I guess the part that was 
confusing me (and still is) is why make-vector worked as expected (by me) 
for my inner vector but not my outer vector. Thanks!


On Sunday, February 10, 2019 at 12:42:53 AM UTC-8, Alex Harsanyi wrote:
>
> This line looks suspicious:
>
>  (define results (make-vector years (make-vector (vector-length 
> fecundity) 0)))
>
> The "(make-vector (vector-length fecundity) 0)" expression will create a 
> single vector, than it creates the outer vector will all elements pointing 
> to it.  It is not a matrix, but a "column" vector where each element is 
> referencing the same row vector.  This means that if you update an element 
> in one of the rows, the same value will "appear" in all other rows. The 
> only row that is different is the first one which you initialize in the 
> line:
>
> (vector-set! results 0 (make-vector (vector-length fecundity) 10))
>
> What you probably want is a vector of vectors, which can be built like this
>
> (define results (for/vector ([index (in-range years)]) (make-vector 
> (vector-length fecundity) 0)))
>
> Alex.
>
>
>
> On Sunday, February 10, 2019 at 3:40:42 PM UTC+8, travis.h...@gmail.com 
> wrote:
>>
>> Hi All,
>>
>> I'm an R programmer that has recently started learning Racket. I decided 
>> to start by trying to create a simple age-structured population model. In 
>> R, I would initialize a matrix and use nested for loops to move through the 
>> elements of the matrix and propagate the population forward through time. 
>> For my first attempt in Racket (
>> https://gist.github.com/hinkelman/3ee6115cdd7f0a4c8f1672b7d8df5c27), I 
>> used for* to loop through a vector of vectors. The code in that gist 
>> doesn't quite work. There is apparently something wrong with how I'm using 
>> vector-set! such that "rows" in my vector of vectors are being updated 
>> prematurely. I would greatly appreciate it if someone could point out what 
>> I'm doing wrong there. I'm also interested in suggestions for alternative 
>> approaches because it seems unlikely that I have written this code in 
>> idiomatic Racket.
>>
>> Thanks,
>>
>> Travis
>>
>> P.S. If it is helpful, here is a gist (
>> https://gist.github.com/hinkelman/d5b8414b0c6383057d7846509a724bbf) with 
>> the R code that I was trying to write in Racket.
>>
>

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Re: [racket-users] Re: nested for loops and suggested alternatives

[Alex Harsanyi]

On Sunday, February 10, 2019 at 4:47:52 PM UTC+8, Philip McGrath wrote:
>
> You may also want to look into the math/array 
>  and math/matrix 
>  libraries.
>


looking at the code, it seems to me that each iteration only the "current" 
and "next" generation are needed.  The best structure might be a list of 
vectors which is constructed step by step -- every iteration a new vector 
is added to this list.   This assumes that the entire "evolution" is needed 
at the end.  If all is needed at the end is the "current" generation, it 
might be more efficient to just use two vectors, the current and next one 
and swap them each iteration.

But before we get into improving the code, let's get it working first :-)

Alex.

 

> -Philip
>
>
> On Sun, Feb 10, 2019 at 3:42 AM Alex Harsanyi  > wrote:
>
>> This line looks suspicious:
>>
>>  (define results (make-vector years (make-vector (vector-length 
>> fecundity) 0)))
>>
>> The "(make-vector (vector-length fecundity) 0)" expression will create a 
>> single vector, than it creates the outer vector will all elements pointing 
>> to it.  It is not a matrix, but a "column" vector where each element is 
>> referencing the same row vector.  This means that if you update an element 
>> in one of the rows, the same value will "appear" in all other rows. The 
>> only row that is different is the first one which you initialize in the 
>> line:
>>
>> (vector-set! results 0 (make-vector (vector-length fecundity) 10))
>>
>> What you probably want is a vector of vectors, which can be built like 
>> this
>>
>> (define results (for/vector ([index (in-range years)]) (make-vector 
>> (vector-length fecundity) 0)))
>>
>> Alex.
>>
>>
>>
>> On Sunday, February 10, 2019 at 3:40:42 PM UTC+8, travis.h...@gmail.com 
>> wrote:
>>>
>>> Hi All,
>>>
>>> I'm an R programmer that has recently started learning Racket. I decided 
>>> to start by trying to create a simple age-structured population model. In 
>>> R, I would initialize a matrix and use nested for loops to move through the 
>>> elements of the matrix and propagate the population forward through time. 
>>> For my first attempt in Racket (
>>> https://gist.github.com/hinkelman/3ee6115cdd7f0a4c8f1672b7d8df5c27), I 
>>> used for* to loop through a vector of vectors. The code in that gist 
>>> doesn't quite work. There is apparently something wrong with how I'm using 
>>> vector-set! such that "rows" in my vector of vectors are being updated 
>>> prematurely. I would greatly appreciate it if someone could point out what 
>>> I'm doing wrong there. I'm also interested in suggestions for alternative 
>>> approaches because it seems unlikely that I have written this code in 
>>> idiomatic Racket.
>>>
>>> Thanks,
>>>
>>> Travis
>>>
>>> P.S. If it is helpful, here is a gist (
>>> https://gist.github.com/hinkelman/d5b8414b0c6383057d7846509a724bbf) 
>>> with the R code that I was trying to write in Racket.
>>>
>> -- 
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>> "Racket Users" group.
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>> email to racket-users...@googlegroups.com .
>> For more options, visit https://groups.google.com/d/optout.
>>
>

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Re: [racket-users] Re: nested for loops and suggested alternatives

[Philip McGrath]

You may also want to look into the math/array
 and math/matrix
 libraries.
-Philip


On Sun, Feb 10, 2019 at 3:42 AM Alex Harsanyi 
wrote:

> This line looks suspicious:
>
>  (define results (make-vector years (make-vector (vector-length
> fecundity) 0)))
>
> The "(make-vector (vector-length fecundity) 0)" expression will create a
> single vector, than it creates the outer vector will all elements pointing
> to it.  It is not a matrix, but a "column" vector where each element is
> referencing the same row vector.  This means that if you update an element
> in one of the rows, the same value will "appear" in all other rows. The
> only row that is different is the first one which you initialize in the
> line:
>
> (vector-set! results 0 (make-vector (vector-length fecundity) 10))
>
> What you probably want is a vector of vectors, which can be built like this
>
> (define results (for/vector ([index (in-range years)]) (make-vector
> (vector-length fecundity) 0)))
>
> Alex.
>
>
>
> On Sunday, February 10, 2019 at 3:40:42 PM UTC+8, travis.h...@gmail.com
> wrote:
>>
>> Hi All,
>>
>> I'm an R programmer that has recently started learning Racket. I decided
>> to start by trying to create a simple age-structured population model. In
>> R, I would initialize a matrix and use nested for loops to move through the
>> elements of the matrix and propagate the population forward through time.
>> For my first attempt in Racket (
>> https://gist.github.com/hinkelman/3ee6115cdd7f0a4c8f1672b7d8df5c27), I
>> used for* to loop through a vector of vectors. The code in that gist
>> doesn't quite work. There is apparently something wrong with how I'm using
>> vector-set! such that "rows" in my vector of vectors are being updated
>> prematurely. I would greatly appreciate it if someone could point out what
>> I'm doing wrong there. I'm also interested in suggestions for alternative
>> approaches because it seems unlikely that I have written this code in
>> idiomatic Racket.
>>
>> Thanks,
>>
>> Travis
>>
>> P.S. If it is helpful, here is a gist (
>> https://gist.github.com/hinkelman/d5b8414b0c6383057d7846509a724bbf) with
>> the R code that I was trying to write in Racket.
>>
> --
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> email to racket-users+unsubscr...@googlegroups.com.
> For more options, visit https://groups.google.com/d/optout.
>

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[racket-users] Re: nested for loops and suggested alternatives

[Alex Harsanyi]

This line looks suspicious:

 (define results (make-vector years (make-vector (vector-length 
fecundity) 0)))

The "(make-vector (vector-length fecundity) 0)" expression will create a 
single vector, than it creates the outer vector will all elements pointing 
to it.  It is not a matrix, but a "column" vector where each element is 
referencing the same row vector.  This means that if you update an element 
in one of the rows, the same value will "appear" in all other rows. The 
only row that is different is the first one which you initialize in the 
line:

(vector-set! results 0 (make-vector (vector-length fecundity) 10))

What you probably want is a vector of vectors, which can be built like this

(define results (for/vector ([index (in-range years)]) (make-vector 
(vector-length fecundity) 0)))

Alex.



On Sunday, February 10, 2019 at 3:40:42 PM UTC+8, travis.h...@gmail.com 
wrote:
>
> Hi All,
>
> I'm an R programmer that has recently started learning Racket. I decided 
> to start by trying to create a simple age-structured population model. In 
> R, I would initialize a matrix and use nested for loops to move through the 
> elements of the matrix and propagate the population forward through time. 
> For my first attempt in Racket (
> https://gist.github.com/hinkelman/3ee6115cdd7f0a4c8f1672b7d8df5c27), I 
> used for* to loop through a vector of vectors. The code in that gist 
> doesn't quite work. There is apparently something wrong with how I'm using 
> vector-set! such that "rows" in my vector of vectors are being updated 
> prematurely. I would greatly appreciate it if someone could point out what 
> I'm doing wrong there. I'm also interested in suggestions for alternative 
> approaches because it seems unlikely that I have written this code in 
> idiomatic Racket.
>
> Thanks,
>
> Travis
>
> P.S. If it is helpful, here is a gist (
> https://gist.github.com/hinkelman/d5b8414b0c6383057d7846509a724bbf) with 
> the R code that I was trying to write in Racket.
>

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