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in reply to Re: Creating a Multi Level Hash from CSV
in thread Creating a Multi Level Hash from CSV

This was so helpful, thank you so much I've really been struggling. I was wondering if you could explain the sub chain{} function? I'm not at all sure what you're doing there, but it works! Also do you have any advice as to what I should do if I want to remove the first row so the header doesn't do what the rest of the hash is doing. Again, really appreciate all your help.
  • Comment on Re^2: Creating a Multi Level Hash from CSV

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Re^3: Creating a Multi Level Hash from CSV
by AnomalousMonk (Bishop) on May 13, 2021 at 20:02 UTC
    ... explain the sub chain{} function ...

    The"Perl Magick" here is recursion; it is not peculiar to Perl in any way.

    sub chain { return @_ > 1 ? { shift() => chain(@_) } : shift(); }
    If there are two or more items in the @_ function argument array (@_ > 1), { shift() => chain(@_) } executes. shift takes the top argument off of @_ and makes it a hash key with the value of whatever the call to chain(@_) returns. Note that chain(@_) is called with whatever remains in the @_ array after one item has been removed by the shift call. This key/value pair is then returned within an anonymous hash reference.

    If there are fewer than two items in the @_ array, the call to chain(@_) simply returns the top item in the array. Note that this does not "properly" handle the case in which the @_ array is empty. What is "proper" handling in this case (if it can even arise)? Only you can figure this out.

    Win8 Strawberry 5.8.9.5 (32) Thu 05/13/2021 15:26:20 C:\@Work\Perl\monks >perl -Mstrict -Mwarnings my %hash; # my ( $top, @rest ) = split /,|\n/; # FIXME faking CSV for testing my ($top, @rest) = qw(foo); $hash{$top} = chain(@rest); use Data::Dump 'dd'; dd \%hash; sub chain { return @_ > 1 ? { shift() => chain(@_) } : shift(); } ^Z { foo => undef }

    ... remove the first row so the header doesn't do what the rest of the hash is doing.

    One might do the following:
        open(my $input, '<:utf8',"input.csv") or die;

        <$input>;  # read and discard one line/record
    (I think Text::CSV can do this for you (it does just about everything else :), but you'll have to check for yourself.)


    Give a man a fish:  <%-{-{-{-<

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