Empty Arrays

An empty array has at least one axis of length 0.

Creating empty arrays

      ⍴ ⍳0
0
      ⍴ 0⍴0
0
      ⍴ 0 4⍴0
0 4

⍳0 produces an empty numeric vector. 0⍴0 reshapes to length 0. 0 4⍴0 creates an empty matrix with 4 columns.

Character vs numeric

Empty character and numeric vectors are distinct by element type but both have shape 0.

      ⍴ ''
0
      ⍴ ⍳0
0

Behaviour with functions

Most scalar functions apply element-wise and produce empty results from empty inputs. Reduce (f/) on an empty array raises DOMAIN ERROR. Scan (f\) on an empty array returns an empty array.