If I have a list of indices with possible repetitions, such as
i=: 1 3 1
how do I convert it to a mask m so that n{m is the number of
occurrences of n in i ?
m=: +/ i =/ i. >: >./ i
0 2 0 1
I can convert from the mask to the (sorted) list of indices with the
I. builtin, eg.
I. m
1 1 3
but is there a simpler way for the conversion to mask? Would it make
sense if I.^:_1 did this?
Ambrus
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