in reply to Re: Back to Remedial Perl for Me: map{} function
in thread Back to Remedial Perl for Me: map{} function

Sorry, merlyn, but the second example *is* turning a list into another list. map is very capable of mapping 1-to-n relations, ie, every element on the right will produce more than one element on the right.

If I read your statement correctly ( and I may not have ), the first use of map isn't correct 

my @first = qw/ one-1 two-2 three-3/;
my %hash  = map { split /-/ } @first; # Which works for me btw
print map { "$_ => $hash{$_}\n" } keys %hash;

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But this usage is correct 
my @first = qw/ one-1 two-2 three-3/;
my @second  = map { split /-/ } @first;
my %hash = @second;  # Legal code, isn't it?
print map { "$_ => $hash{$_}\n" } keys %hash;

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How else is map supposed to make @first into @second except by performing an action on every element of @first?

I am not arguing that a foreach wouldn't be appropriate here. If that is what works, by all means use it. But if I am not supposed to use map when I want an action on every element of an array, doesn't it make more sense to say 

@second = @first;

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because that seems to be the only option you have left me with this statement.

Would you be kind enough to expand on your answer so I can figure out what I missed?

TIA
mikfire

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Re: Re: Re: Back to Remedial Perl for Me: map{} function
by merlyn (Sage) on Dec 15, 2000 at 20:35 UTC
    I wasn't commenting on either of those. I was commenting on the original poster's last example: 
    if ($access) { 
    foreach (@{$access}) { 
        $set{$_->[0]} = $_->[1]; 
    } 
}

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    That's just fine as it is. No need for a map. In fact, a map would be difficult here, unless we presume %set is already empty before we get here.

    -- Randal L. Schwartz, Perl hacker

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[d/l]
      Ahh. I got scope locked and assumed that you were referring to the map examples, not the foreach loop.

      Thanks
      mikfire

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Re: Re: Re: Back to Remedial Perl for Me: map{} function
by $code or die (Deacon) on Dec 15, 2000 at 21:05 UTC
    Out of interest, why does this (both examples) print: 
    one => 1
three => 3
two => 2

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    and not: 
    one => 1
two => 2
three => 3

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[reply]
[d/l]
[select]

      Because hashes are unordered.

      --
      <http://www.dave.org.uk>

      "Perl makes the fun jobs fun
      and the boring jobs bearable" - me

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        "unsorted" would be more precise...the elements in the hash do have an order, but not not "in the order" that we might put them.
[reply]
        That's what I thought, but it did the same order every time I ran it, so it seems that there is some order (i.e. it's not completely random). Was just wondering how perl decides to order it. Even Data::Dumping the hash gives the same order!
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