Elisp: Sequence. Take, Drop, Slice

Take First N

seq-take

(seq-take SEQUENCE N)

take first n.

(seq-take (vector 1 2 3 4 5) 3)
;; [1 2 3]

seq-take-while

(seq-take-while PRED SEQUENCE)

take elements until PRED returns nil.

(seq-take-while
 (lambda (x) (< x 4))
 (vector 1 2 3 4 5))
;; [1 2 3]

Remove First N

• seq-drop → remove first n.
• seq-drop-while → remove first n, with a condition to stop.

Get Subsequence (aka slice)

seq-subseq

(seq-subseq SEQUENCE START &optional END)

Get a subsequence specified by start index and end index (exclude the end index). End index default to get all.

Index can be negative. It means count from right.

(seq-subseq (vector 0 1 2 3 4 5 6 7) 3)
;; [3 4 5 6 7]

;; not including end
(seq-subseq (vector 0 1 2 3 4 5 6 7) 3 6)
;; [3 4 5]