## strange result with map and apply

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fdb
Posts: 65
Joined: Sat Nov 09, 2013 8:49 pm

### strange result with map and apply

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``````> (map (apply +) '((0 1 2) (3 4 5)))
((0 1 2) (3 4 5))
> (map (fn(x) (apply + x)) '((0 1 2) (3 4 5)))
(3 12)
``````
Why doesn't the first example work?

bairui
Posts: 64
Joined: Sun May 06, 2012 2:04 am
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### Re: strange result with map and apply

With:

Code: Select all

``(map (apply max) '((0 1 2) (3 4 5)))``
we see the expected error:

ERR: missing argument in function max

I don't know why we don't see this with the + function, but the solution to both cases is to use curry:

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``(map (curry apply +) '((0 1 2) (3 4 5)))``

Lutz
Posts: 5285
Joined: Thu Sep 26, 2002 4:45 pm
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### Re: strange result with map and apply

Like in Scneme (+) or (apply +) evaluates to 0. So your map expression maps 0 onto two lists.
Using a number as operator is implicit resting. 0 gives you back the whole list.
Try also (map (apply *) '((0 1 2) (3 4 5))) to prove the point. Like in Scheme (*) gives 1.

So using curry for what you want is the right thing.

bairui
Posts: 64
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### Re: strange result with map and apply

Ah, that makes sense. Thanks, Lutz.

fdb
Posts: 65
Joined: Sat Nov 09, 2013 8:49 pm

### Re: strange result with map and apply

Thanks a lot bairui and Luts! Hadn't used curry before.

Another question i just encountered is how to change all items in a list in one go, for example:

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``````(set-ref-all "2" '(("1" "2" "3") ("4")) (int \$it))
(("1" 2 "3") ("4"))
``````
Works but i want to change all the strings to integers in one go but couldn't find an expression which matches
all the strings, see below some examples i tried but didn't work

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``````> (set-ref-all '((*)) '(("1" "2" "3") ("4")) (int \$it))
nil
> (set-ref-all '(?) '(("1" "2" "3") ("4")) (int \$it))
nil
> (set-ref-all '(*) '(("1" "2" "3") ("4")) (int \$it))
nil
> (set-ref-all '(+) '(("1" "2" "3") ("4")) (int \$it))
nil
> (set-ref-all ? '(("1" "2" "3") ("4")) (int \$it))
nil
> (set-ref-all * '(("1" "2" "3") ("4")) (int \$it))
nil

``````

cormullion
Posts: 2037
Joined: Tue Nov 29, 2005 8:28 pm
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### Re: strange result with map and apply

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``````(set-ref-all '(*) '(("1" "2" "3") ("4")) (map int \$it) match)
;-> ((1 2 3) (4))
``````
I admit that match is the one area in newLISP that I always fail to get right in the first few attempts... :)

bairui
Posts: 64
Joined: Sun May 06, 2012 2:04 am
Location: China
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### Re: strange result with map and apply

Not as veratile as cormullion's match solution, but works for the given example:

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``(map (curry map int) '(("1" "2" "3") ("4")))``

fdb
Posts: 65
Joined: Sat Nov 09, 2013 8:49 pm

### Re: strange result with map and apply

Thx!

I understood the function from bairui directly (why didn't i think of that..) but i had to look in the documentation to understand cormullion's solution and then i saw in the documentation this example:
(set-ref-all '(oranges *) data (list (first \$it) (apply + (rest \$it))) match) ....

Great docs, just have to read them more carefully next time.