⍳ — Index generator / Index of⍳N generates 1…N. Dimensions are nonnegative integers; exact input gives exact coordinates.
⍳4 ⍝ 1 2 3 4
⍳3x ⍝ 1x 2x 3x
A shape vector generates an array of coordinate vectors.
⍳2 2 ⍝ 2 2⍴(1 1⋄ 1 2⋄ 2 1⋄ 2 2)
X⍳Y finds the first matching major cell in X for each cell of Y. Not found: 1+≢X. Uses tolerant matching and returns exact positions.
'abc'⍳'cabz' ⍝ 3x 1x 2x 4x
'abc'⍳'b' ⍝ 2x
'abc'⍳⊂'b' ⍝ 2x
A single query returns an atom. Batch axes supply the result shape. Enclose an array-valued query to search for it as one item.
C←'cat' 'dog'
C⍳⊂'dog' ⍝ 2x
C⍳,⊂'dog' ⍝ ,2x
m←3 2⍴10 20 30 40 50 60
m⍳30 40 ⍝ 2x
m⍳1 2⍴30 40 ⍝ ,2x
m⍳2 2⍴30 40 10 20 ⍝ 2x 1x