Re: [R] dist like function but where you can configure the method
Function designdist() in package vegan lets you define your own distance
measure, but it does not let you simply provide a function as your original
request indicated. Function distance() in package ecodist() indicates that it
is written to make it simple to add new distance functions, but warns that it
is not efficient for large matrices.
David Carlson
-Original Message-
From: r-help-boun...@r-project.org [mailto:r-help-boun...@r-project.org] On
Behalf Of Witold E Wolski
Sent: Friday, May 16, 2014 3:00 PM
To: Rui Barradas
Cc: Jari Oksanen; r-h...@stat.math.ethz.ch; Barry Rowlingson
Subject: Re: [R] dist like function but where you can configure the method
Ouch,
First : my question was not how to implement dist but if there is a more
generic dist function than stats:dist.
Secondly: ks.test is ment as a placeholder (see the comment in the code I did
send) for any other function taking two vector arguments.
Third: I do subscribe to the idea that a function call is easier to read and
understand than a for loop. @Bert apply is a native C function and the loop is
not interpreted AFAIK
@Rui @Barry @Jari What do you benchmark? an empty loop?
Look at the trivial benchmarks below: _apply_ clearly outperforms a for loop in
R , It always has, it outperforms even an empty for
# an empty unrealistic for loop as suggested by Rui , Barry and Jari
f1 - function(n){
for(i in 1:n){
for(j in 1:n){
}
}}
myfunc = function(x,y=x){x-y}
# a for loop which does actually something
f2 - function(n){
mm - matrix(0,ncol=n,nrow=n)
for(i in 1:n){
for(j in 1:n){
mm[i,j] = myfunc(i,j)
}
}
return(mm)
}
# and array
f3 = function(n){
res = rep(0,n*n)
for(i in 1:(n*n))
{
res[i] = myfunc(i)
}
}
n = 1000
system.time(f1(n))
system.time(f2(n))
system.time(f3(n))
system.time(apply(t(1:(n*n)),1,myfunc))
system.time(f1(n))
User System verstrichen
0.280.000.28
system.time(f2(n))
User System verstrichen
6.800.007.09
system.time(f3(n))
User System verstrichen
5.830.005.98
system.time(apply(t(1:(n*n)),1,myfunc))
User System verstrichen
0.190.000.19
On 16 May 2014 20:55, Rui Barradas ruipbarra...@sapo.pt wrote:
Hello,
The compiler package is good at speeding up for loops but in this case
the gain is neglectable. The ks test is the real time problem.
library(compiler)
f1 - function(n){
for(i in 1:100){
for(i in 1:100){
ks.test(runif(100),runif(100))
}
}
}
f1.c - cmpfun(f1)
system.time(f1())
user system elapsed
3.500.003.53
system.time(f1.c())
user system elapsed
3.470.003.48
Rui Barradas
Em 16-05-2014 17:12, Barry Rowlingson escreveu:
On Fri, May 16, 2014 at 4:46 PM, Witold E Wolski wewol...@gmail.com
wrote:
Dear Jari,
Thanks for your reply...
The overhead would be
2 for loops
for(i in 1:dim(x)[2])
for(j in i:dim(x)[2])
isn't it? Or are you seeing a different way to implement it?
A for loop is pretty expensive in R. Therefore I am looking for an
implementation similar to apply or lapply were the iteration is made
in native code.
No, a for loop is not pretty expensive in R -- at least not compared
to doing a k-s test:
system.time(for(i in 1:1){ks.test(runif(100),runif(100))})
user system elapsed
3.680 0.012 3.697
3.68 seconds to do 1 ks tests (and generate 200 runifs)
system.time(for(i in 1:1){})
user system elapsed
0.000 0.000 0.001
0.000s time to do 1 loops. Oh lets nest it for fun:
system.time(for(i in 1:100){for(i in
1:100){ks.test(runif(100),runif(100))}})
user system elapsed
3.692 0.004 3.701
no different. Even a ks-test with only 5 items is taking me 2.2 seconds.
Moral: don't worry about the for loops.
Barry
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Witold Eryk Wolski
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] dist like function but where you can configure the method
Witold E Wolski wewolski at gmail.com writes:
Looking for an fast dist implementation
where I could pass my own dist function to the method parameter
i.e.
mydistfun = function(x,y){
return(ks.test(x,y)$p.value) #some mystique implementation
}
wow = dist(data,method=mydistfun)
I think it is best to write that function yourself.
The dist object is a vector corresponding to a lower triangle
(without the diagonal) of a symmetric matrix and with attributes.
The attributes are class which should be c(mydist, dist), Size
which is the length(x), Labels (optional) which are the
names of your items and if given, should have length(x),
call = match.call(), Diag = FALSE, Upper = FALSE and method name.
All you need is a vector with attributes.
All this will add very little overhead to your calculation, so
for all practical purposes this implementation is just as fast as
is your mystique implementation of pairwise distances. Your
example (ks.test()) probably would be pretty slow. If you can
vectorize your distance, it can be really fast, even if you
calculate the full symmetric matrix and throw away the diagonal and
upper triangle.
Cheers, Jari Oksanen
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] dist like function but where you can configure the method
Dear Jari,
Thanks for your reply...
The overhead would be
2 for loops
for(i in 1:dim(x)[2])
for(j in i:dim(x)[2])
isn't it? Or are you seeing a different way to implement it?
A for loop is pretty expensive in R. Therefore I am looking for an
implementation similar to apply or lapply were the iteration is made
in native code.
On 16 May 2014 15:57, Jari Oksanen jari.oksa...@oulu.fi wrote:
Witold E Wolski wewolski at gmail.com writes:
Looking for an fast dist implementation
where I could pass my own dist function to the method parameter
i.e.
mydistfun = function(x,y){
return(ks.test(x,y)$p.value) #some mystique implementation
}
wow = dist(data,method=mydistfun)
I think it is best to write that function yourself.
The dist object is a vector corresponding to a lower triangle
(without the diagonal) of a symmetric matrix and with attributes.
The attributes are class which should be c(mydist, dist), Size
which is the length(x), Labels (optional) which are the
names of your items and if given, should have length(x),
call = match.call(), Diag = FALSE, Upper = FALSE and method name.
All you need is a vector with attributes.
All this will add very little overhead to your calculation, so
for all practical purposes this implementation is just as fast as
is your mystique implementation of pairwise distances. Your
example (ks.test()) probably would be pretty slow. If you can
vectorize your distance, it can be really fast, even if you
calculate the full symmetric matrix and throw away the diagonal and
upper triangle.
Cheers, Jari Oksanen
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Witold Eryk Wolski
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] dist like function but where you can configure the method
On Fri, May 16, 2014 at 4:46 PM, Witold E Wolski wewol...@gmail.com wrote:
Dear Jari,
Thanks for your reply...
The overhead would be
2 for loops
for(i in 1:dim(x)[2])
for(j in i:dim(x)[2])
isn't it? Or are you seeing a different way to implement it?
A for loop is pretty expensive in R. Therefore I am looking for an
implementation similar to apply or lapply were the iteration is made
in native code.
No, a for loop is not pretty expensive in R -- at least not compared
to doing a k-s test:
system.time(for(i in 1:1){ks.test(runif(100),runif(100))})
user system elapsed
3.680 0.012 3.697
3.68 seconds to do 1 ks tests (and generate 200 runifs)
system.time(for(i in 1:1){})
user system elapsed
0.000 0.000 0.001
0.000s time to do 1 loops. Oh lets nest it for fun:
system.time(for(i in 1:100){for(i in 1:100){ks.test(runif(100),runif(100))}})
user system elapsed
3.692 0.004 3.701
no different. Even a ks-test with only 5 items is taking me 2.2 seconds.
Moral: don't worry about the for loops.
Barry
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] dist like function but where you can configure the method
Yes, ... and further
apply-type functions still have to loop at the interpreter level, and
generally take about the same time as their translation to for loops
(with suitable caveats for this kind of vague assertion). Their chief
advantage is readability and adherence to R's functional paradigm
(again with suitable caveats).
Alternatively, byte code compilation with the compiler package **may**
(significantly) improve speed, but it very much depends ...
Cheers,
Bert
Bert Gunter
Genentech Nonclinical Biostatistics
(650) 467-7374
Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom.
H. Gilbert Welch
On Fri, May 16, 2014 at 9:12 AM, Barry Rowlingson
b.rowling...@lancaster.ac.uk wrote:
On Fri, May 16, 2014 at 4:46 PM, Witold E Wolski wewol...@gmail.com wrote:
Dear Jari,
Thanks for your reply...
The overhead would be
2 for loops
for(i in 1:dim(x)[2])
for(j in i:dim(x)[2])
isn't it? Or are you seeing a different way to implement it?
A for loop is pretty expensive in R. Therefore I am looking for an
implementation similar to apply or lapply were the iteration is made
in native code.
No, a for loop is not pretty expensive in R -- at least not compared
to doing a k-s test:
system.time(for(i in 1:1){ks.test(runif(100),runif(100))})
user system elapsed
3.680 0.012 3.697
3.68 seconds to do 1 ks tests (and generate 200 runifs)
system.time(for(i in 1:1){})
user system elapsed
0.000 0.000 0.001
0.000s time to do 1 loops. Oh lets nest it for fun:
system.time(for(i in 1:100){for(i in
1:100){ks.test(runif(100),runif(100))}})
user system elapsed
3.692 0.004 3.701
no different. Even a ks-test with only 5 items is taking me 2.2 seconds.
Moral: don't worry about the for loops.
Barry
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] dist like function but where you can configure the method
I did not regard the loops as the overhead but a part of the process. Overhead
is setting attributes. The loop is not so very expensive compared to ks.test().
You can always replace the loop with an apply on the vector of indices, but
about the only way to speed up calculations is to use parallel processing
(parLapply, parSapply, parRapply functions of the parallel processing.
I wrote about vectorization: that would be faster, but it cannot be done
blindly to just any function, but you must deconstruct the function to see if
it can decomposed into operations of vectors. In vegan:::designdist we do that
for some function types, but you really must *think* about the function you are
using to know if you can write it in vectorized form. It is not automatic.
Cheers, Jari Oksanen
On 16/05/2014, at 18:46 PM, Witold E Wolski wrote:
Dear Jari,
Thanks for your reply...
The overhead would be
2 for loops
for(i in 1:dim(x)[2])
for(j in i:dim(x)[2])
isn't it? Or are you seeing a different way to implement it?
A for loop is pretty expensive in R. Therefore I am looking for an
implementation similar to apply or lapply were the iteration is made
in native code.
On 16 May 2014 15:57, Jari Oksanen jari.oksa...@oulu.fi wrote:
Witold E Wolski wewolski at gmail.com writes:
Looking for an fast dist implementation
where I could pass my own dist function to the method parameter
i.e.
mydistfun = function(x,y){
return(ks.test(x,y)$p.value) #some mystique implementation
}
wow = dist(data,method=mydistfun)
I think it is best to write that function yourself.
The dist object is a vector corresponding to a lower triangle
(without the diagonal) of a symmetric matrix and with attributes.
The attributes are class which should be c(mydist, dist), Size
which is the length(x), Labels (optional) which are the
names of your items and if given, should have length(x),
call = match.call(), Diag = FALSE, Upper = FALSE and method name.
All you need is a vector with attributes.
All this will add very little overhead to your calculation, so
for all practical purposes this implementation is just as fast as
is your mystique implementation of pairwise distances. Your
example (ks.test()) probably would be pretty slow. If you can
vectorize your distance, it can be really fast, even if you
calculate the full symmetric matrix and throw away the diagonal and
upper triangle.
Cheers, Jari Oksanen
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Witold Eryk Wolski
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] dist like function but where you can configure the method
Hello,
The compiler package is good at speeding up for loops but in this case
the gain is neglectable. The ks test is the real time problem.
library(compiler)
f1 - function(n){
for(i in 1:100){
for(i in 1:100){
ks.test(runif(100),runif(100))
}
}
}
f1.c - cmpfun(f1)
system.time(f1())
user system elapsed
3.500.003.53
system.time(f1.c())
user system elapsed
3.470.003.48
Rui Barradas
Em 16-05-2014 17:12, Barry Rowlingson escreveu:
On Fri, May 16, 2014 at 4:46 PM, Witold E Wolski wewol...@gmail.com wrote:
Dear Jari,
Thanks for your reply...
The overhead would be
2 for loops
for(i in 1:dim(x)[2])
for(j in i:dim(x)[2])
isn't it? Or are you seeing a different way to implement it?
A for loop is pretty expensive in R. Therefore I am looking for an
implementation similar to apply or lapply were the iteration is made
in native code.
No, a for loop is not pretty expensive in R -- at least not compared
to doing a k-s test:
system.time(for(i in 1:1){ks.test(runif(100),runif(100))})
user system elapsed
3.680 0.012 3.697
3.68 seconds to do 1 ks tests (and generate 200 runifs)
system.time(for(i in 1:1){})
user system elapsed
0.000 0.000 0.001
0.000s time to do 1 loops. Oh lets nest it for fun:
system.time(for(i in 1:100){for(i in
1:100){ks.test(runif(100),runif(100))}})
user system elapsed
3.692 0.004 3.701
no different. Even a ks-test with only 5 items is taking me 2.2 seconds.
Moral: don't worry about the for loops.
Barry
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] dist like function but where you can configure the method
Ouch,
First : my question was not how to implement dist but if there is a
more generic dist function than stats:dist.
Secondly: ks.test is ment as a placeholder (see the comment in the
code I did send) for any other function taking two vector arguments.
Third: I do subscribe to the idea that a function call is easier to
read and understand than a for loop. @Bert apply is a native C
function and the loop is not interpreted AFAIK
@Rui @Barry @Jari What do you benchmark? an empty loop?
Look at the trivial benchmarks below: _apply_ clearly outperforms a
for loop in R , It always has, it outperforms even an empty for
# an empty unrealistic for loop as suggested by Rui , Barry and Jari
f1 - function(n){
for(i in 1:n){
for(j in 1:n){
}
}}
myfunc = function(x,y=x){x-y}
# a for loop which does actually something
f2 - function(n){
mm - matrix(0,ncol=n,nrow=n)
for(i in 1:n){
for(j in 1:n){
mm[i,j] = myfunc(i,j)
}
}
return(mm)
}
# and array
f3 = function(n){
res = rep(0,n*n)
for(i in 1:(n*n))
{
res[i] = myfunc(i)
}
}
n = 1000
system.time(f1(n))
system.time(f2(n))
system.time(f3(n))
system.time(apply(t(1:(n*n)),1,myfunc))
system.time(f1(n))
User System verstrichen
0.280.000.28
system.time(f2(n))
User System verstrichen
6.800.007.09
system.time(f3(n))
User System verstrichen
5.830.005.98
system.time(apply(t(1:(n*n)),1,myfunc))
User System verstrichen
0.190.000.19
On 16 May 2014 20:55, Rui Barradas ruipbarra...@sapo.pt wrote:
Hello,
The compiler package is good at speeding up for loops but in this case the
gain is neglectable. The ks test is the real time problem.
library(compiler)
f1 - function(n){
for(i in 1:100){
for(i in 1:100){
ks.test(runif(100),runif(100))
}
}
}
f1.c - cmpfun(f1)
system.time(f1())
user system elapsed
3.500.003.53
system.time(f1.c())
user system elapsed
3.470.003.48
Rui Barradas
Em 16-05-2014 17:12, Barry Rowlingson escreveu:
On Fri, May 16, 2014 at 4:46 PM, Witold E Wolski wewol...@gmail.com
wrote:
Dear Jari,
Thanks for your reply...
The overhead would be
2 for loops
for(i in 1:dim(x)[2])
for(j in i:dim(x)[2])
isn't it? Or are you seeing a different way to implement it?
A for loop is pretty expensive in R. Therefore I am looking for an
implementation similar to apply or lapply were the iteration is made
in native code.
No, a for loop is not pretty expensive in R -- at least not compared
to doing a k-s test:
system.time(for(i in 1:1){ks.test(runif(100),runif(100))})
user system elapsed
3.680 0.012 3.697
3.68 seconds to do 1 ks tests (and generate 200 runifs)
system.time(for(i in 1:1){})
user system elapsed
0.000 0.000 0.001
0.000s time to do 1 loops. Oh lets nest it for fun:
system.time(for(i in 1:100){for(i in
1:100){ks.test(runif(100),runif(100))}})
user system elapsed
3.692 0.004 3.701
no different. Even a ks-test with only 5 items is taking me 2.2 seconds.
Moral: don't worry about the for loops.
Barry
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Witold Eryk Wolski
__
R-help@r-project.org mailing list
https://stat.ethz.ch/mailman/listinfo/r-help
PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
Re: [R] dist like function but where you can configure the method
system.time(apply(t(1:(n*n)),1,myfunc))
User System verstrichen
0.190.000.19
That calls 'myfunc' exactly once:
system.time(apply(t(1:(3*3)), 1, print))
[1] 1 2 3 4 5 6 7 8 9
user system elapsed
0 0 0
Bill Dunlap
TIBCO Software
wdunlap tibco.com
On Fri, May 16, 2014 at 1:00 PM, Witold E Wolski wewol...@gmail.com wrote:
Ouch,
First : my question was not how to implement dist but if there is a
more generic dist function than stats:dist.
Secondly: ks.test is ment as a placeholder (see the comment in the
code I did send) for any other function taking two vector arguments.
Third: I do subscribe to the idea that a function call is easier to
read and understand than a for loop. @Bert apply is a native C
function and the loop is not interpreted AFAIK
@Rui @Barry @Jari What do you benchmark? an empty loop?
Look at the trivial benchmarks below: _apply_ clearly outperforms a
for loop in R , It always has, it outperforms even an empty for
# an empty unrealistic for loop as suggested by Rui , Barry and Jari
f1 - function(n){
for(i in 1:n){
for(j in 1:n){
}
}}
myfunc = function(x,y=x){x-y}
# a for loop which does actually something
f2 - function(n){
mm - matrix(0,ncol=n,nrow=n)
for(i in 1:n){
for(j in 1:n){
mm[i,j] = myfunc(i,j)
}
}
return(mm)
}
# and array
f3 = function(n){
res = rep(0,n*n)
for(i in 1:(n*n))
{
res[i] = myfunc(i)
}
}
n = 1000
system.time(f1(n))
system.time(f2(n))
system.time(f3(n))
system.time(apply(t(1:(n*n)),1,myfunc))
system.time(f1(n))
User System verstrichen
0.280.000.28
system.time(f2(n))
User System verstrichen
6.800.007.09
system.time(f3(n))
User System verstrichen
5.830.005.98
system.time(apply(t(1:(n*n)),1,myfunc))
User System verstrichen
0.190.000.19
On 16 May 2014 20:55, Rui Barradas ruipbarra...@sapo.pt wrote:
Hello,
The compiler package is good at speeding up for loops but in this case the
gain is neglectable. The ks test is the real time problem.
library(compiler)
f1 - function(n){
for(i in 1:100){
for(i in 1:100){
ks.test(runif(100),runif(100))
}
}
}
f1.c - cmpfun(f1)
system.time(f1())
user system elapsed
3.500.003.53
system.time(f1.c())
user system elapsed
3.470.003.48
Rui Barradas
Em 16-05-2014 17:12, Barry Rowlingson escreveu:
On Fri, May 16, 2014 at 4:46 PM, Witold E Wolski wewol...@gmail.com
wrote:
Dear Jari,
Thanks for your reply...
The overhead would be
2 for loops
for(i in 1:dim(x)[2])
for(j in i:dim(x)[2])
isn't it? Or are you seeing a different way to implement it?
A for loop is pretty expensive in R. Therefore I am looking for an
implementation similar to apply or lapply were the iteration is made
in native code.
No, a for loop is not pretty expensive in R -- at least not compared
to doing a k-s test:
system.time(for(i in 1:1){ks.test(runif(100),runif(100))})
user system elapsed
3.680 0.012 3.697
3.68 seconds to do 1 ks tests (and generate 200 runifs)
system.time(for(i in 1:1){})
user system elapsed
0.000 0.000 0.001
0.000s time to do 1 loops. Oh lets nest it for fun:
system.time(for(i in 1:100){for(i in
1:100){ks.test(runif(100),runif(100))}})
user system elapsed
3.692 0.004 3.701
no different. Even a ks-test with only 5 items is taking me 2.2 seconds.
Moral: don't worry about the for loops.
Barry
__
R-help@r-project.org mailing list
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--
Witold Eryk Wolski
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Re: [R] dist like function but where you can configure the method
If the apply() call is not empty, its contents must of course be
interpreted. That's where the time goes.
system.time(for(i in 1:1e6)rnorm(1))
user system elapsed
5.250.005.29
system.time(lapply(1:1e6,rnorm,n=1))
user system elapsed
9.640.019.72
system.time(vapply(1:1e6,rnorm,FUN.VALUE=0,n=1))
user system elapsed
5.690.005.73
I rest my case.
Cheers,
Bert
Bert Gunter
Genentech Nonclinical Biostatistics
(650) 467-7374
Data is not information. Information is not knowledge. And knowledge
is certainly not wisdom.
H. Gilbert Welch
On Fri, May 16, 2014 at 1:00 PM, Witold E Wolski wewol...@gmail.com wrote:
Ouch,
First : my question was not how to implement dist but if there is a
more generic dist function than stats:dist.
Secondly: ks.test is ment as a placeholder (see the comment in the
code I did send) for any other function taking two vector arguments.
Third: I do subscribe to the idea that a function call is easier to
read and understand than a for loop. @Bert apply is a native C
function and the loop is not interpreted AFAIK
@Rui @Barry @Jari What do you benchmark? an empty loop?
Look at the trivial benchmarks below: _apply_ clearly outperforms a
for loop in R , It always has, it outperforms even an empty for
# an empty unrealistic for loop as suggested by Rui , Barry and Jari
f1 - function(n){
for(i in 1:n){
for(j in 1:n){
}
}}
myfunc = function(x,y=x){x-y}
# a for loop which does actually something
f2 - function(n){
mm - matrix(0,ncol=n,nrow=n)
for(i in 1:n){
for(j in 1:n){
mm[i,j] = myfunc(i,j)
}
}
return(mm)
}
# and array
f3 = function(n){
res = rep(0,n*n)
for(i in 1:(n*n))
{
res[i] = myfunc(i)
}
}
n = 1000
system.time(f1(n))
system.time(f2(n))
system.time(f3(n))
system.time(apply(t(1:(n*n)),1,myfunc))
system.time(f1(n))
User System verstrichen
0.280.000.28
system.time(f2(n))
User System verstrichen
6.800.007.09
system.time(f3(n))
User System verstrichen
5.830.005.98
system.time(apply(t(1:(n*n)),1,myfunc))
User System verstrichen
0.190.000.19
On 16 May 2014 20:55, Rui Barradas ruipbarra...@sapo.pt wrote:
Hello,
The compiler package is good at speeding up for loops but in this case the
gain is neglectable. The ks test is the real time problem.
library(compiler)
f1 - function(n){
for(i in 1:100){
for(i in 1:100){
ks.test(runif(100),runif(100))
}
}
}
f1.c - cmpfun(f1)
system.time(f1())
user system elapsed
3.500.003.53
system.time(f1.c())
user system elapsed
3.470.003.48
Rui Barradas
Em 16-05-2014 17:12, Barry Rowlingson escreveu:
On Fri, May 16, 2014 at 4:46 PM, Witold E Wolski wewol...@gmail.com
wrote:
Dear Jari,
Thanks for your reply...
The overhead would be
2 for loops
for(i in 1:dim(x)[2])
for(j in i:dim(x)[2])
isn't it? Or are you seeing a different way to implement it?
A for loop is pretty expensive in R. Therefore I am looking for an
implementation similar to apply or lapply were the iteration is made
in native code.
No, a for loop is not pretty expensive in R -- at least not compared
to doing a k-s test:
system.time(for(i in 1:1){ks.test(runif(100),runif(100))})
user system elapsed
3.680 0.012 3.697
3.68 seconds to do 1 ks tests (and generate 200 runifs)
system.time(for(i in 1:1){})
user system elapsed
0.000 0.000 0.001
0.000s time to do 1 loops. Oh lets nest it for fun:
system.time(for(i in 1:100){for(i in
1:100){ks.test(runif(100),runif(100))}})
user system elapsed
3.692 0.004 3.701
no different. Even a ks-test with only 5 items is taking me 2.2 seconds.
Moral: don't worry about the for loops.
Barry
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PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
--
Witold Eryk Wolski
__
R-help@r-project.org mailing list
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
__
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PLEASE do read the posting guide http://www.R-project.org/posting-guide.html
and provide commented, minimal, self-contained, reproducible code.
