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Re: Problem with position and find (cl)


From: Thierry Volpiatto
Subject: Re: Problem with position and find (cl)
Date: Sat, 21 Jun 2008 14:38:32 +0200
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/23.0.60 (gnu/linux)

Marc Tfardy <address@hidden> writes:

> Marc Tfardy schrieb:
>> Thierry Volpiatto schrieb:
>>> Florian Beck <address@hidden> writes:
>>>
>>>> Marc Tfardy <address@hidden> writes:
>>>>
>>>>> Marc Tfardy schrieb:
>>>>>> I try with:
>>>>>> (member '(2) '((1) (2) (3) (4)))
>>>> `member' tests the components: ›2‹ ist always equal (in the sense
>>>> of »eq«) to ›2‹
>>>>
>>>> Compare:
>>>>
>>>> (memq '(2) '((1) (2) (3) (4)))
>>>> (eq 2 2)
>>>> (eq '(2) '(2))
>>>>
>>>>>> and this gives a expectet results ((2) (3) (4)), but:
>>>>>> (find '(2) '((1) (2) (3) (4)))
>>>>>> or
>>>>>> (position '(2) '((1) (2) (3) (4)))
>>>>>>
>>>>>> returns nil. Why?
>>>> Because  the first and the second »(2)« have the same components but are
>>>> *different* lists.
>>>>
>>>>> But this works:
>>>>>
>>>>> (position '(2) '((1) (2) (3) (4)) :test (lambda (x y) (eq (car x) (car
>>>>> y))))
>>>>>
>>
>>> position default test is 'eq, try 'equal
>>
>> Thanks! It works with equal. But I have another problem.
>> find (and find-if) returns only first match. Is there another
>> function that returns all matched elements. Some example:
>>
>> (find-if-all (lambda (x) (if (eq (nth 2 x) 'byte) t nil)) '((1.1 "x"
>> int) (2.2 "y" byte) (3.3 "q" int) (4.4 "b" byte) (5.5 "a" float)))
>>
>> should returns:
>> ((2.2 "y" byte) (4.4 "b" byte))
>>
>> I found in cl-*.el nothing like this. Any hints?
>
>
> I found some "strange" solution:
>
> (remove-if-not (lambda (x) (if (eq (nth 2 x) 'byte) t nil)) '((1.1 "x"
> int) (2.2 "y" byte) (3.3 "q" int) (4.4 "b" byte) (5.5 "a" float)))
>
> but with:
> (fset 'find-all 'remove-if-not)
> or:
> (defalias 'find-all 'remove-if-not)
>
> (a propos - what is the right method?) - it looks good and
> works like expected.
Is it something like that you are looking for ?
,----
| ELISP> (setq A '((2 "a" byte)
|                  (3.2 "b" float)
|                  (4 "c" byte)
|                  (6 "d" int)
|                  (8 "e" byte)))
| ((2 "a" byte)
|  (3.2 "b" float)
|  (4 "c" byte)
|  (6 "d" int)
|  (8 "e" byte))
| 
| ELISP> (defun find-all (item lis)
|          (let ((temp-list nil))
|            (dolist (x lis)
|              (when (equal (nth 2 x) item)
|                (push x temp-list)))
|            temp-list))
| find-all
| ELISP> (find-all 'byte A)
| ((8 "e" byte)
|  (4 "c" byte)
|  (2 "a" byte))
`----


-- 
A + Thierry
Pub key: http://pgp.mit.edu




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