This is likely to make little sense to people who don't use the Perl Data Language module but here goes anyway...

I have a piddle containing a sequence of numbers from 0-9 and another piddle containing a subset of these numbers... ie:
my $a = sequence(10);
print $a;
[0,1,2,3,4,5,6,7,8,9]
my $b = pdl(2,5,7);
print $b;
[2,5,7]

[download]
What I want to do is search within the larger piddle for values that match any of those in the second piddle, and return their index values. So in this case I'd end up with a piddle that looks like [3,6,8].
'which' seems like the logical structure for this but it doesn't work for more than one value... ie:
my $z = which($a==$b(1));
print $z;
[3]

[download]
But 
my $z = which($a==$b);

[download]
fails completely. Any ideas?

In reply to perl PDL question by nickschurch

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
to format your post, it's "PerlMonks-approved HTML":


  • Posts are HTML formatted. Put <p> </p> tags around your paragraphs. Put <code> </code> tags around your code and data!
  • Titles consisting of a single word are discouraged, and in most cases are disallowed outright.
  • Read Where should I post X? if you're not absolutely sure you're posting in the right place.
  • Please read these before you post! —
  • Posts may use any of the Perl Monks Approved HTML tags:
    a, abbr, b, big, blockquote, br, caption, center, col, colgroup, dd, del, details, div, dl, dt, em, font, h1, h2, h3, h4, h5, h6, hr, i, ins, li, ol, p, pre, readmore, small, span, spoiler, strike, strong, sub, summary, sup, table, tbody, td, tfoot, th, thead, tr, tt, u, ul, wbr
  • You may need to use entities for some characters, as follows. (Exception: Within code tags, you can put the characters literally.)
            For:     Use:
    & &amp;
    < &lt;
    > &gt;
    [ &#91;
    ] &#93;
  • Link using PerlMonks shortcuts! What shortcuts can I use for linking?
  • See Writeup Formatting Tips and other pages linked from there for more info.