in reply to Re^2: Help understand why this grep does not work
in thread Help understand why this grep does not work

I wondered about building a hash for this. What would be the best way? Are you thinking something like this is better: 
my %data_hash = map { /(\w\s+\d)/ => $_ } @data2;

for my $key ( %data_hash ) {
    print "$data_hash{$key}\n" if grep { /^$key/ } @data1;
}

[download]

I also wondered about anchoring that match. In earlier versions, I did anchor it. But, I wasn't sure if it was necessary given the data set. I think I'll add it back as it's probably safer.

Thanks for the advice!

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Re^4: Help understand why this grep does not work
by LanX (Saint) on Nov 02, 2013 at 16:21 UTC
    well kind of ... but your code only works if the first 2 chars combinations are unique otherwise you need to push into a HoA.

    I think the or-ed regex I've shown you is better, as long as @data1 is known from the beginning and doesn't change dynamically.

    Cheers Rolf

    ( addicted to the Perl Programming Language)

[reply]

      Yes, this is why I didn't do that in the first place. Although with the data I have listed I think this would work, if I had to expand it and there weren't unique values, you're right - this wouldn't work so well. I think your 'or-ed regex' is indeed better.

      For the sake of argument (I'm just playing around trying to get better a handling data in Perl and the map function), what's the best way to create a hash of arrays with this data? I can't seem to create the data structure with a map. I know this won't work as it overwrites the values on each pass:

      my %data_hash = map { /^(\w\s+\d)/ => [$_] } @data2;

      [download]

      But, I can't seem to figure out how to create a hash of arrays with the map function. Maybe it's not possible or not the best way?

[reply]
[d/l]
        OK, these two three possibilities seem to do it, but by far not as performant as the or-ed regex.

          DB<126> %hash = map { my ($m)=/^(\w\s+\d)/; $m => [ grep {/^$m/} @da
+ta2 ] } @data1 
 => ("a 1", [], "a 2", ["a 2 Y"], "a 3", ["a 3 R"])

  DB<127> %hash = map { my $k=$_ ; $k => [ grep {/^$k/} @data2 ] } map
+ { /^(\w\s+\d)/} @data1 
 => ("a 1", [], "a 2", ["a 2 Y"], "a 3", ["a 3 R"])

  DB<128> %hash = map { /^(\w\s+\d)/; $1 => [ grep {/^$1/} @data2 ] } 
+@data1
 => ("a 1", [], "a 2", ["a 2 Y"], "a 3", ["a 3 R"])

        [download]

        update

        see also Generating Hash-of-List using map?

        Cheers Rolf

        ( addicted to the Perl Programming Language)

[reply]
[d/l]

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