Re: sorting a list

[Pascal Bourguignon]

Seweryn Kokot <skokot@o2.pl> writes:

> Assume I have a list
>
> '(("abc" "xxsx") 
>   ("zdfa" "xxsx") 
>   ("dddbc" "xxsx") 
>   ("cabc" "xxsx"))
>
> How to sort the list according to the first element in the lists so to
> get
>
> '(("abc" "xxsx")
>   ("cabc" "xxsx")
>   ("dddbc" "xxsx")
>   ("zdfa" "xxsx"))

(require 'cl)
(sort* list (function string<) :key (function first))

Note that sort and sort* are destructive of the original list.  
You must not give it a literal list.

(defun f-good ()
 (let ((list '(("abc" "xxsx") 
               ("zdfa" "xxsx") 
               ("dddbc" "xxsx") 
               ("cabc" "xxsx"))))
  (list (second list)
        (first (sort* (copy-list list)
                      (function string<) :key (function first))))))

(defun f-bad ()
 (let ((list '(("abc" "xxsx") 
               ("zdfa" "xxsx") 
               ("dddbc" "xxsx") 
               ("cabc" "xxsx"))))
  (list (second list)
        (first (sort* list
                      (function string<) :key (function first))))))

(list (f-good) (f-good))
--> ((#1=("zdfa" "xxsx") #2=("abc" "xxsx")) (#1# #2#))

(list (f-bad) (f-bad))
--> ((("zdfa" "xxsx") #1=("abc" "xxsx")) (("cabc" "xxsx") #1#))


-- 
__Pascal Bourguignon__                     http://www.informatimago.com/

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