[Perldl] problems with which()

[Vikas N Kumar]

Hi

I am stumped by the problems I face with simple conditionals in using
the which() function. I have tried many different ways in trying to
solve it but none of them give me the result I want.

Here is a sample:

    use PDL;
    # a random list of values that are above and below 0
    my $a = randsym(100) - 0.5;

    # create a lag of 1
    my $idx = xvals($a->dims) - 1;
    $i = $i->setbadif($i < 0)->setbadtoval(0); # can this be more elegant ?

    # find all the positions where $a[i] > 0 and $a[i - 1] < 0
    # in essence where $a crosses the zero line
    my $b = zeroes($a->dims);
    my $b_idx = which($a > 0 && $a->index($i) < 0);

    # set those points as 1
    $b->index($b_idx) .= 1;

Everytime I run this I get "multielement piddle in conditional
expression" errors.

I have not been able to find an elegant solution to this problem. I
cannot seem to create a mask that has more than 1 piddle comparisons.

Please help.

Thanks
Vikas


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