Filter nested list if item exists

[Browning_Zed]

Hi All,
I again had a need to process the list. There was a need to filter the list if a certain item position exists.

In details:
in each nested list, all items can be numbered according to position like this:

;;   items:   1  2  3     1   2   3      1   2   3      1  2   3        
(setq lst '(("1" a nil) ("2" nil 20.0) (nil nil 30.0) (nil nil 40.0)))

now how to create a new list from the original list if an item with a certain number exists? For example, when executing a function in which the first argument is a list of item number positions, then:

(setq lst '(("1" a nil) ("2" nil 20.0) (nil nil 30.0) (nil nil 40.0)))

(somefunction '(1) lst)
;; =>> '(("1" a nil) ("2" nil 20.0))

(somefunction '(2) lst)
;; =>> '(("1" a nil))

(somefunction '(2 3) lst)
;; =>> '(("1" a nil) ("2" nil 20.0) (nil nil 30.0) (nil nil 40.0))

[Kent1Cooper]

For the first two:

(defun TEST (lst pos) (vl-remove-if-not '(lambda (x) (nth (1- pos) x)) lst))

(test lst 1)
(("1" A nil) ("2" nil 20.0))

(test lst 2)
(("1" A nil))

(test lst 3)
(("2" nil 20.0) (nil nil 30.0) (nil nil 40.0))

That's with a single position number [as just a number].  I'll have to think about the third situation a little....

[ronjonp · Accepted solution]

Adding to Kent's solution to take care of the 3rd scenario:

(defun test (lst pos)
  (vl-remove-if-not '(lambda (x) (vl-some '(lambda (y) (nth (1- y) x)) pos)) lst)
)
(setq l '(("1" a nil) ("2" nil 20.0) (nil nil 30.0) (nil nil 40.0)("$" nil nil)))
(test l '(2 3))
;; (("1" A nil) ("2" nil 20.0) (nil nil 30.0) (nil nil 40.0))

[Browning_Zed]

Thank you for your help, dear sirs.

[ronjonp]

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@Browning_Zed wrote:

Thank you for your help, dear sirs.

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Glad to help 🍻