A really good PDL library for operating on vectors is PDL::VectorValued. Indeed, it's so good that we're just discussing incorporating it into main PDL (see https://github.com/moocow-the-bovine/PDL-VectorValued/issues/5).

The particular operation you'd want here is probably vsearchvec.

In reply to Re^3: Counting PDL vectors in a PDL matrix by etj
in thread Counting PDL vectors in a PDL matrix by mxb

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