List to Columns

[Jonathan Handojo]

Hi guys,

 

Who has the shortest way to do something like the reverse of (apply 'append assoc_list)?

 

I'm simply looking for a function that can sort one long list into an association list of x items each.

 

So for example, if your function is (list-to-columns lst cols), then calling:

 

(list-to-columns '(0 1 2 3 4 5 6 7 8 9 10 11 12 13 14) 4)

 

will return ((0 1 2 3) (4 5 6 7) (8 9 10 11) (12 13 14))

 

Thanks,

Jonathan Handojo

[Grrr]

Look for a GroupByN subfoo somewhere here.

[Jonathan Handojo]

Found it. Thanks for that... I kinda thought it should be a recursive function, but I didn't know how to write one XD

[Lee Mac]

Here's my take on it: Group List by Number

[Jonathan Handojo]

Didn't know that existed in your website. I didn't know what it was called so...

 

When I actually wrote an iterative approach before posting this question (thinking that it was a non-efficient function), it was actually more or less the same as your iterative approach... which is why I hope there was a recursive approach somewhere (because I'm weak in recursive functions, but willing to find examples to learn from). Thanks Lee.

[Grrr]

1 hour ago, Jonathan Handojo said:

which is why I hope there was a recursive approach somewhere (because I'm weak in recursive functions, but willing to find examples to learn from)

 

Back in the time was playin' around with such -

(setq pL '(1 2 3 4 5 6 7 8 9 10 11 12 13 14 15))
('((f L)(f L)) '(( L ) (if L (cons (mapcar ''( (x) (nth x L)) '(0 1 2)) (f (cdddr L))))) pL)

Now I'm so tight that I can't take the time to write out a decent reply to my own threads :sad:

[Jonathan Handojo]

This may seem off the topic, but I'm pretty sure it's online somewhere, I just can't find it... Do you also happen to know of a function that can list all possible combinations of a list if you're supplied an association list?

[Jonathan Handojo]

Never mind, I figured it out... I went through all sorts of hell to figure it out, lost half my hair

 

(defun JH:listcombination (lst)
    (if (null lst) '(nil)
	(apply 'append
	       (mapcar
		   '(lambda (x)
			(mapcar
			    '(lambda (y)
				 (cons x y)
				 )
			    (JH:listcombination (cdr lst))
			    )
			)
		   (car lst)
		   )
	       )
	)
    )

 

I was simply toying around, though I'm not sure how it actually ended up with the desired result.

[Lee Mac]

Some others:

 

https://www.theswamp.org/index.php?topic=2694

https://www.theswamp.org/index.php?topic=47435.msg524472#msg524472

https://www.theswamp.org/index.php?topic=30434.msg360831#msg360831

http://lee-mac.com/permutations.html

 

Edited April 29, 2020 by Lee Mac

[hanhphuc]

On 4/29/2020 at 11:52 AM, Jonathan Handojo said:

 

(defun JH:listcombination (lst)

 

I was simply toying around, though I'm not sure how it actually ended up with the desired result.

 

nice! you can trace your function in the console