Hi folks,

I'm using PDL (the Perl Data Language, pdl.perl.org) to manipulate a Very Large dataset.

I'm having quite a bit of trouble with the correct syntax for threading, can't seem to get it right.

Right now I'm doing a lookup, where an old value gets turned into a new value. There's a one-to-one relationship between old values and new values. Currently I'm doing this using a normal hash, like this: 

    my @old_values = list($pdl_oldvalues);
    my @new_values = map $hash_lookup->{$_}, @old_values; 
    my $pdl_newvalues = pdl(\@new_values);

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I'd like to do this using PDL threading if I can, because I want it to go quicker (there are a lot of values), but I can't find the right way to do it.

I've tried: 

    my $pdl_newvals = $hash_lookup->{$pdl_oldvals};

[download]
but sadly that doesn't work. I've tried using $pdl_oldvals->thread(0) and $pdl_oldvals->dummy(0) but they don't work either.

I've also tried turning the hash into a two-row pdl, with keys on one row and values on the other row, then taking a slice from that pdl to get the values. That should certainly work with pdl threading... but I can't get it to. :(

Suggestions, and examples of correct syntax for doing this kind of thing in pdl, very much appreciated.

All the best, andye.

PS where "doesn't work" = either a syntax error, or runs but produces the wrong values...

In reply to Hash-type lookup in PDL by andye

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