http://www.perlmonks.org?node_id=991208


in reply to Re^3: filtering an array
in thread filtering an array

i see. so if my array @positions is already defined and created, do i need to loop over all the values in @positions and then execute the code you posted?

something like:

 for (@positions) {@positions = grep $_->[1] =~ /ac/i, @positions;}

and then:

 for (@positions) {@positions = map $_->[0], @positions;}

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Re^5: filtering an array
by philiprbrenan (Monk) on Sep 01, 2012 at 23:03 UTC

    Likewise, the for is unnecessary in this code too:

    for (@positions) {@positions = map $_->[0], @positions;}

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    It should just be:

    @positions = map $_->[0], @positions;

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    because map iterates over the array you give it. Even better, you could write:

    $_ = $_->[0] for @positions;

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    here we are making the for implicit in map explicit.

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      perl still has a problem with this:

      @positions = grep $_->[1] =~ /ac/i, @positions;

      with the same error Use of uninitialized value in pattern match (m//)

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[d/l]

        One or more of the elements of the array @positions is undefined. The easiest way to check this is like this:

        use Data::Dump qw(pp);

pp([@positions]);

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        This will give you a printout of the value of each element in array @positions. I expect we will see that some are "undef" meaning undefined. It will be these elements that are causing the problem.

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Re^5: filtering an array
by philiprbrenan (Monk) on Sep 01, 2012 at 22:59 UTC

    You do not need the for becuase grep loops over the array you give it. Please change:

     
 for (@positions) {@positions = grep $_->[1] =~ /ac/i, @positions;}

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    to:

     
 @positions = grep $_->[1] =~ /ac/i, @positions;

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[d/l]
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      right, but the error still persists. what here isn't defined?
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