Indices

Z←⍸R returns an integer vector identical to R/⍳>R.

R is a scalar or vector of non-negative integers.

Z is an integer vector of length +/Rwhose values are R/⍳>R where monadic > is the Tally function.

This feature encapsulates a very common idiom in one symbol.

For example, in origin-0

      ⍸1 0 1 1 1 0 1
0 2 3 4 6
      ⍸2 3 4
0 0 1 1 1 2 2 2 2