vivekvp has asked for the wisdom of the Perl Monks concerning the following question:

Hello, I have to arrays read in from a file called @a and @b. Both have the save number of elements... Can I use them in one FOREACH loop or do I need 2? i.e. 

foreach $a(@a) {
print "a- $a    b - $b \n"
}

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Or do I have to... 
$cnt=@a;
for ($count=0;$count<$cnt;$count++) {
print "a $a[$count]   b $b[$count] \n";
}

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Any way to do that with a foreach? Thanks, V He who laughs last, doesn't get the joke.

Replies are listed 'Best First'.
Re: VVP:arrays of the same size.
by dragonchild (Archbishop) on Mar 20, 2002 at 20:40 UTC
    There's a few ways to do it. The most intuitive is the following: 
    for (my $i = 0; $i < @a; $i++) {
    # Do stuff with @a and @b
}

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    Another way would be to make a temporary hash and use each. This means you don't care what order stuff is done in, so long as the Nth element of @a is processed with the Nth element of @b. 
    my %temp;
@temp{@a} = @b;
while (my ($a_val, $b_val) = each %temp) {
    # Do stuff with $a_val and $b_val
}

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    The first is clearer and easier to work with. Plus, it allows the addition of some @c later on in the future.

    Now, if these are parallel arrays, you might want to consider doing the following: 

    use mapcar; # This is on a node [tye] posted somewhere on PM

my @temp_arr = mapcar { \@_ } (\@a, \@b);
foreach my $vals (@temp_arr) {
    # Do stuff with $vals->[0] (from @a) and $vals->[1] (from @b)
}

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    That makes it very clear they are parallel arrays. *shrugs* YMMV

    ------
    We are the carpenters and bricklayers of the Information Age.

    Don't go borrowing trouble. For programmers, this means Worry only about what you need to implement.

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Re: VVP:arrays of the same size.
by dreadpiratepeter (Priest) on Mar 20, 2002 at 20:41 UTC
    look at mapcar. It allows you to iterate through multiple arrays simultaneously.

    -pete
    "I am Jack's utter lack of disbelief"
[reply]
      You probably mean this mapcar.

      /prakash

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