What is happening is that your 2 arrays are being threaded over, however the dimensions don't match. The case that works has a 1 element pdl, which can be threaded over because pdl replicates length 1 dimensions as many times as necessary. Try this: 
my $a = sequence(10)->dummy;
my $b = pdl(2,5,7);
my $z = which(sumover($a == $b));

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This inserts a dummy dimension into $a so that $a is dimensionality (10,1) and $b is dimensionality (1,3). Dimensions of length 1 get threaded over nicely. The sumover is there to take away 1 of the dimensions (otherwise you get location in $a times location in $b) for matches

In reply to Re: perl PDL question by Anonymous Monk
in thread perl PDL question by nickschurch

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