in reply to Re: Re: Link a hash and an array
in thread Link a hash and an array

But, of course, that does not work exactly like that

It would probably help if you used syntactically valid Perl code. If you did, you might be surprised to find that what you have works fine. Here I've gone through the trouble to port it for you:

#!/usr/bin/perl
use strict;    # safety checks
use warnings;  # useful hints
use Data::Dumper;

# notice the use of 'my' to declare a lexical scope
my @Address=qw(type firstname lastname streetaddress city zip);
my @Phone=qw(type name phonenumber);

sub ReadStuff {
    # instead of using funny global variables, scope the 
    # hash within the subroutine, and return a reference at
    # the end
    my %Stuff;

    # $_[0]       is the first element of the array @_
    # eq          is the string equality test
    # @h{@k} = @v is the syntax for hash slices
    if    ($_[0] eq 'addr')  { @Stuff{@Address} = @_ }
    elsif ($_[0] eq 'phone') { @Stuff{@Phone}   = @_ }

    # return a reference (as mentioned before)
    return \%Stuff;
}


# let's quote our list elements this time
my @data1 = ('addr', 'bob', 'smith', '1234 main st', 'anytown', '20500
+');
my $stuff1 = ReadStuff(@data1);

my @data2 = ('phone', 'bob', 'smith', '212-555-1212');
my $stuff2 = ReadStuff(@data2);

# dump the results from both runs
print Dumper $stuff1;
print Dumper $stuff2;

[download]

Update: while this code does work, it doesn't quite do what your original question asks. That said, what you have here is probably exactly what I would suggest -- that is, keep the data in one place, and a list of keys in the other to tie it together. Using the structures this code creates, you could, for example, do $Stuff1->{$Address[4]} to get the field from $Stuff1 that corresponds to the key at index 4 from @Address. (whew! try saying that 5 times fast!)

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Re: Re: Re: Re: Link a hash and an array
by SkipHuffman (Monk) on Mar 12, 2004 at 15:45 UTC

    Thank you.

    I am currently crawling through the replies and making sense of them. I had to spend a couple of hours with use strict and use warnings turned on to clean up my lousy syntax.

    Obviously I am a bit of a novice (to Perl, I have been whacking keys and writing bad code for about fifteen years). Yes, I have the Llama, access to a Camel, and the Cheeta.

    Thank you all.

[reply]
Re: Re: Re: Re: Link a hash and an array
by SkipHuffman (Monk) on Mar 12, 2004 at 16:23 UTC

    Thank you very much for the recodeing. I have found it very edifying. It does work, and work quite well, and I am adding it to my mental perl toolset. But it does not do exactly what I need to do.

    What I need to do is store the data in an array and access it from a hash. I need to be able to make a change using the a hash variable and have it affect the array variable.

    You have shown me how to copy the data from an array into a hash using key names from another array. A valuable function, but not what I need.

    Thank you,

    Skip

[reply]
      But it does not do exactly what I need to do.

      Yeah, that's what I pointed out in my Update. But as I said there, I think it might be a bad idea to keep the actual data in two places. Even using references, there's the chance that the references get stale and you're pointing to different data. I would strongly suggest picking either the hash, or the array, and keep the data there. Then, in the other one, store nothing but indexes (unique keys) that show where to get the data.

      Perhaps an example will make it more obvious. Here I will store the actual data in arrays, but have a lookup table to map hash keys to array indexes:

      my %index = (firstname => 0,
             lastname  => 1,
             address   => 2,
             town      => 3,
             zip       => 4);

my @array1 = ("Bob", "Smith", "1234 Main St", "Anytown", "20500");
my @array2 = ("Joe", "Blow", "4321 Street Ln", "Notown", "20050");

print "First name (from array1): $array1[ $index{firstname} ]\n";
print "Address    (from array2): $array2[ $index{address}   ]\n";

      [download]

      Notice that we can fairly easily access the data via key name, but we don't have to worry about making sure two disperate structures stay in sync. The only thing we have to worry about is the keys-to-indexes map getting out of date -- but hopefully that is a rare problem.

      Another approach that you might find interesting is to just use an array, and have constants to store the array indexes. This would give the advantage of not quite as verbose a syntax. Here's an example of that:

      use constant { FIRSTNAME => 0,
               LASTNAME  => 1,
               ADDRESS   => 2,
               TOWN      => 3,
               ZIP       => 4 };

my @array1 = ("Bob", "Smith", "1234 Main St", "Anytown", "20500");
my @array2 = ("Joe", "Blow", "4321 Street Ln", "Notown", "20050");

print "First name (from array1): $array1[ FIRSTNAME ]\n";
print "Address    (from array2): $array2[ ADDRESS   ]\n";

      [download]
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