Re: [racket-users] Funtional programming and the maximum of something

2016-10-22 Thread Daniel Prager 
> circle of recursion

I reckon "helix of recursion" would be a more helpful image.

Dan

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Re: [racket-users] Funtional programming and the maximum of something

2016-10-22 Thread Robby Findler 
On Sat, Oct 22, 2016 at 3:05 PM,   wrote:
> Robby Findler  [16-10-22 21:28]:
>> You need to follow the design recipe to solve a problem like this. You
>> data is clear: [Listof [Listof Real]] and [Listof Real]. Next up:
>> examples. Do you have examples of the inputs and outputs you want for
>> this function?
>>
>> Robby
>>
>> On Sat, Oct 22, 2016 at 2:03 PM,   wrote:
>> > Hi,
>> >
>> > (I am still a newbie ... )
>> >
>> > If I remember  one rule of functional programming
>> > correctly, it says:
>> > Instead of changeing data - create new data.
>> >
>> > Suppose I have a list of list. Each "sublist" is
>> > made of a greater amount (but identical count) of
>> > exact numbers (integers).
>> >
>> > I want to process these data recursively and if
>> > all is done I want to get back a list of numbers
>> > (same count of numbers as in each sublist), which
>> > represents the maximum of all numbers of that "position"
>> > in all sublists.
>> >
>> > If I want to make this purely (may be inpractical) functional,..
>> > I see (as a newbie) the following problem.
>> > From two numbers as input I have to build a maximum and
>> > have to feed that into the next circle of recursion as
>> > one of the numbers to compare.
>> > Each time a new maximum is found I have to overwrite the
>> > old one.
>> > This contradicts the rule "Dont change data, create new one."
>> >
>> > How can I get out of this?
>> >
>> > Cheers
>> > Meino
>> >
>> >
>> >
>> >
>> > --
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>
> Hi Robby, hi Phillip, hi Justin,
>
> thanks a lot for your help... !!! :)
> This gives me mind twisters (but this was one reason
> for me to learn racket ;)
>
> So, I think my "knot in the logic" was
> to process one sublist at each circle of recursion
> and being urged to create a temporary maximum with
> each recursion that way, which gets possibly overwritten
> in the next circle with a new temporary maximum.
>
> The 'apply map' creates - as far as I can understand it -
> the maximum from ALL numbers of a certain position of all sublists
> in one go. It creates on ONE maximum and no temporary resuls.
> That's clever :)
>
> Cheers,
> Meino
>
> From the Dictionary of Adanced Programming:
> "Recursion, the: (see "Recursion" )
>
>

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Re: [racket-users] Funtional programming and the maximum of something

2016-10-22 Thread Justin Zamora 
A clue to the answer is in your statement that you "feed that [maximum]
into the next circle of recursion." Notice that you're not overwriting the
value in the current call, you're creating a new value that you feed into
the new call in the "next circle". So the old one isn't being overwritten
at all.

Justin

On Oct 22, 2016 3:15 PM,  wrote:

> Hi,
>
> (I am still a newbie ... )
>
> If I remember  one rule of functional programming
> correctly, it says:
> Instead of changeing data - create new data.
>
> Suppose I have a list of list. Each "sublist" is
> made of a greater amount (but identical count) of
> exact numbers (integers).
>
> I want to process these data recursively and if
> all is done I want to get back a list of numbers
> (same count of numbers as in each sublist), which
> represents the maximum of all numbers of that "position"
> in all sublists.
>
> If I want to make this purely (may be inpractical) functional,..
> I see (as a newbie) the following problem.
> From two numbers as input I have to build a maximum and
> have to feed that into the next circle of recursion as
> one of the numbers to compare.
> Each time a new maximum is found I have to overwrite the
> old one.
> This contradicts the rule "Dont change data, create new one."
>
> How can I get out of this?
>
> Cheers
> Meino
>
>
>
>
> --
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Re: [racket-users] Funtional programming and the maximum of something

2016-10-22 Thread Philip McGrath 
I'm not sure if I understand what you're tying to do correctly, but here's
one way to do it (or one way to do something, at least):

(define (process-list-of-lists list-of-lists)
  (apply map
(λ args
   (apply max args))
list-of-lists))
(process-list-of-lists
  `((55 1 2)
(8 13 7)
(3 9 42
;; returns '(55 13 42)


Of course, you could also use explicit recursion instead of map and apply,
but you don't "overwrite" the result of a previous recursive call in either
case.

On Sat, Oct 22, 2016 at 2:04 PM  wrote:

> Hi,
>
> (I am still a newbie ... )
>
> If I remember  one rule of functional programming
> correctly, it says:
> Instead of changeing data - create new data.
>
> Suppose I have a list of list. Each "sublist" is
> made of a greater amount (but identical count) of
> exact numbers (integers).
>
> I want to process these data recursively and if
> all is done I want to get back a list of numbers
> (same count of numbers as in each sublist), which
> represents the maximum of all numbers of that "position"
> in all sublists.
>
> If I want to make this purely (may be inpractical) functional,..
> I see (as a newbie) the following problem.
> From two numbers as input I have to build a maximum and
> have to feed that into the next circle of recursion as
> one of the numbers to compare.
> Each time a new maximum is found I have to overwrite the
> old one.
> This contradicts the rule "Dont change data, create new one."
>
> How can I get out of this?
>
> Cheers
> Meino
>
>
>
>
> --
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> To unsubscribe from this group and stop receiving emails from it, send an
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Re: [racket-users] Funtional programming and the maximum of something

2016-10-22 Thread Robby Findler 
You need to follow the design recipe to solve a problem like this. You
data is clear: [Listof [Listof Real]] and [Listof Real]. Next up:
examples. Do you have examples of the inputs and outputs you want for
this function?

Robby

On Sat, Oct 22, 2016 at 2:03 PM,   wrote:
> Hi,
>
> (I am still a newbie ... )
>
> If I remember  one rule of functional programming
> correctly, it says:
> Instead of changeing data - create new data.
>
> Suppose I have a list of list. Each "sublist" is
> made of a greater amount (but identical count) of
> exact numbers (integers).
>
> I want to process these data recursively and if
> all is done I want to get back a list of numbers
> (same count of numbers as in each sublist), which
> represents the maximum of all numbers of that "position"
> in all sublists.
>
> If I want to make this purely (may be inpractical) functional,..
> I see (as a newbie) the following problem.
> From two numbers as input I have to build a maximum and
> have to feed that into the next circle of recursion as
> one of the numbers to compare.
> Each time a new maximum is found I have to overwrite the
> old one.
> This contradicts the rule "Dont change data, create new one."
>
> How can I get out of this?
>
> Cheers
> Meino
>
>
>
>
> --
> You received this message because you are subscribed to the Google Groups 
> "Racket Users" group.
> To unsubscribe from this group and stop receiving emails from it, send an 
> email to racket-users+unsubscr...@googlegroups.com.
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[racket-users] Funtional programming and the maximum of something

2016-10-22 Thread Meino . Cramer 
Hi,

(I am still a newbie ... )

If I remember  one rule of functional programming
correctly, it says: 
Instead of changeing data - create new data.

Suppose I have a list of list. Each "sublist" is 
made of a greater amount (but identical count) of 
exact numbers (integers).

I want to process these data recursively and if
all is done I want to get back a list of numbers
(same count of numbers as in each sublist), which
represents the maximum of all numbers of that "position"
in all sublists.

If I want to make this purely (may be inpractical) functional,..
I see (as a newbie) the following problem.
>From two numbers as input I have to build a maximum and
have to feed that into the next circle of recursion as
one of the numbers to compare.
Each time a new maximum is found I have to overwrite the
old one.
This contradicts the rule "Dont change data, create new one."

How can I get out of this?

Cheers
Meino




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