↑ — First / Take

Function. Keys: Alt-k. Hanzi: 取. Ranks: ∞ monadic, 1 ∞ dyadic

↑Y returns the first major item, like 0⊃Y. On an enclosure it returns the contained value. An empty leading axis gives a cell of fill.

↑[[1 2] [3 4 5]]  ⍝ 1 2
↑2 3⍴⍳6ₓ           ⍝ [0 1 2]ₓ
↑⊂7               ⍝ 7
↑0 3⍴0            ⍝ 0 0 0

N↑Y takes leading items; negative N takes from the end. Overtake inserts fill. ⍠ can choose the fill, for Take and for First.

4↑1 2              ⍝ 1 2 0 0
¯4↑1 2             ⍝ 0 0 1 2

Vector counts apply to successive leading axes. N↑⍠K Y applies the counts to axes K.

1 2↑2 3⍴⍳6ₓ         ⍝ 1 2⍴[0 1]ₓ

Inverse

↑⁻Y encloses Y.

↑⁻5   ⍝ ⊂5