Re^3: Hash-type lookup in PDL


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Re^3: Hash-type lookup in PDL

by lin0 (Curate)

on Jan 05, 2007 at 19:52 UTC ( [id://593197]=note: print w/replies, xml )

Need Help??

in reply to Re^2: Hash-type lookup in PDL
in thread Hash-type lookup in PDL

Hi andye,

If your lookup table is rather small, you could try this code:

#!/usr/bin/perl

use warnings;
use strict;
use PDL;

my $x = sequence(5); print "$x \n";

my @pdl_keys   =     (0,    1,   2,      3,   4);
my @pdl_values =     (101, 69,  42,  10042,  99);

my $y = zeroes(5);
foreach my $i (0..@pdl_keys-1){
    my $indx = which($x == $pdl_keys[$i]);
    $y->dice($indx) .= $pdl_values[$i];
}
print "$y \n";
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I hope this helps

Cheers,

lin0

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Re^4: Hash-type lookup in PDL
by andye (Curate) on Jan 06, 2007 at 18:17 UTC

zentara

lin0

Well, I went ahead and did it with my original approach of: convert the pdl to a perl list, then use a perl hash to look it up, then convert it back again. The batch job finished about half a day later, so it's an academic issue now really.

Still, (as a note for for posterity) there seem really to be two options being discussed here:

Either:

- a PDL lookup table, using which() or dice() to look up one value at a time (slow on big datasets),

- convert all the values in advance, as per zentara's code above...

Neither's ideal really... could be that converting to a perl scalar and using a hash is actually the best thing.

Thanks for your help, and best wishes,
andye

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