Mapcar for (if (= ....

Bill Tillman · 发表于 2022-7-6 06:27:35

I have an exercise this morning I'm working on and thought why not make use of the time to learn more about mapcar/lambda.

I have four variables:

If any of these variables contains the value of "Y" I want to take some action. I've been doing this in the past:

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(if (or (= front "Y") (= back "Y") (= rside "Y") (= lside "Y")) (setq a "Y"))

All the examples I've searched through so far show how to add 1, subtract 2, strcase, etc... How would one run this process through mapcar/lambda to achieve the same results? Or would this not be a good example of where to use mapcar in lieu of the above (if (or statement?

pBe · 发表于 2022-7-6 06:47:43

Based on your example for value assign to variable A

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(setq a (vl-some             '(lambda (v)                    (if (eq (eval v) "Y")                          "Y"))             '(front back rside lside)))

or if you want to see what variable has the value "Y"

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(vl-some     '(lambda (v)            (if (eq (eval v) "Y")                  v))     '(front back rside lside))

EDIT: Man, i saw a similar sugesstion by Ron at the swamp.

BlackBox · 发表于 2022-7-6 07:07:06

Consider:

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(setq a      (car        (vl-remove-if-not          (function (lambda (x) (= "Y" x)))          (list front back rside lside)        )      ))

Speed test:

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(defun _foo1 () (vl-some   '(lambda (v)      (if (eq (eval v) "Y")        "Y"      )    )   (list front back rside lside) ))(defun _foo2 () (car   (vl-remove-if-not     (function (lambda (x) (= x "Y")))     (list front back rside lside)   ) ))

... Result from console:

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_FOO1 _FOO2 _$ (bench '(_foo1 _foo2) '() 10000)_FOO1Elapsed: 733Average: 0.0733_FOO2Elapsed: 63Average: 0.0063_$

pBe · 发表于 2022-7-6 07:17:09

I'm sold

BlackBox · 发表于 2022-7-6 07:29:28

Cheers, pBe

[编程交流] Mapcar for (if (= ....

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