⍸
Interval Index r←x⍸y
r
is the index of each corresponding cell of y
in the intervals defined by the major cells of x
, which is assumed to be sorted: cells of y
before all cells of x
are labeled 0
, cells of y
between the first cell and the second cell of x
are labeled 1
, ..., cells of y
after all cells of x
are labeled ≢x
.