Re: Regarding Hashes of Arrays

They're both incorrect. If you'd use warnings you'd get a warning from the first construct.

$hash{$id} = (1,2,3); will set $hash{$id} = 3 (the last element in the list).

and $hash{$id} = @temp; will set $hash{$id} = 3 (the length of @temp).

You cannot literally make a hash with arrays as the values in Perl, you need array-references:

$hash{$id} = [1,2,3]; # [ ... ] creates an anonymous array ref
@temp = (1,2,3);
$hash{$id} = \@temp; # \ makes an explicit reference to @temp
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Note that \(1,2,3) will make a list of references to 1, 2 and 3, so don't use that.

If you want to read one of the values from the array ref you do:

$x = ${$hash{$id}}[0];
# or
$x = $hash{$id}[0];
# or
$x = $hash{$id}->[0];
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I like the last syntax best, because it makes it clear that there is a reference (more or less equivalent to a "pointer" in C speak) involved.

If you want to whole list of values from the array, you can do:

my @values = @{$hash{$id}};
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perlref has a lot of info about this.

"What should it profit a man, if he should win a flame war, yet lose his cool?"

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Re^2: Regarding Hashes of Arrays by hardburn (Abbot) on Aug 10, 2004 at 20:16 UTC
I like the last syntax best, because it makes it clear that there is a reference (more or less equivalent to a "pointer" in C speak) involved. The fact that there is a multi-dimentional datastructure should already make it assumed there are references involved. Or do you know of a way to do complex datastructures in Perl without references? "There is no shame in being self-taught, only in not trying to learn in the first place." -- Atrus, Myst: The Book of D'ni.	[reply]
Re^3: Regarding Hashes of Arrays by Joost (Canon) on Aug 10, 2004 at 20:30 UTC
do you know of a way to do complex datastructures in Perl without references? Yes. `$hash{1,2,3,4} = 'one'; $hash{1,2,3,5} = 'two'; print $hash{1,2,3,4},$hash{1,2,3,5}; __END__ onetwo` [download] leftovers from perl4, I know, but it's still valid perl. "What should it profit a man, if he should win a flame war, yet lose his cool?"	[reply] [d/l]
Re^4: Regarding Hashes of Arrays by hardburn (Abbot) on Aug 10, 2004 at 20:51 UTC
/me shudders at code above I still say the `->` is unnecessary, since if you're using real datastructures in Perl, the references part should be assumed. "There is no shame in being self-taught, only in not trying to learn in the first place." -- Atrus, Myst: The Book of D'ni.	[reply] [d/l]
Re^5: Regarding Hashes of Arrays by Joost (Canon) on Aug 10, 2004 at 20:59 UTC