= — Classify / Equal

Function. Ranks: ∞ monadic, 0 0 dyadic

=Y self-classifies the major cells of Y. The result has a row for each distinct cell, in order of first occurrence, and a column for each cell of Y. An entry is $t where its column’s cell equals its row’s cell.

="aba"            ⍝ [$t $f $t⋄$f $t $f]

X=Y tests equality, pervasively. NaN equals nothing, as IEEE 754 defines.

1 2 3=2            ⍝ $f $t $f
0.3=0.1+0.2        ⍝ $t
"abc"='b'          ⍝ $f $t $f

See tolerance and whole-array match ≡.

Inverse

On Booleans, = is its own inverse with either argument fixed.

1 0=⁻¹1 1   ⍝ $t $f