Iterating over hash elements (was: Sorry to bother you)

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

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Re: Iterating over hash elements by BrowserUk (Patriarch) on Nov 17, 2002 at 22:01 UTC
`my $totalHours = 0; $totalHours += $main{$month}{johndoe}for my $month (keys %main);` [download] Okay you lot, get your wings on the left, halos on the right. It's one size fits all, and "No!", you can't have a different color. Pick up your cloud down the end and "Yes" if you get allocated a grey one they *are* a bit damp under foot, but someone has to get them. Get used to the wings fast cos its an 8 hour day...unless the Govenor calls for a cyclone or hurricane, in which case 16 hour shifts are mandatory. Just be grateful that you arrived just as the tornado season finished. Them buggers are real work.	[reply] [d/l]
Re: Summing values of subkey in a HoH by Aristotle (Chancellor) on Nov 18, 2002 at 00:09 UTC
Why does everyone's code build a list of keys when they don't use them for anything but accessing the values? `my $total; $total += $_->{$member} for values %main;` [download] (At this this point it's obvious that `%main` needs a better name.) Makeshifts last the longest.	[reply] [d/l]
Re: Iterating over hash elements by Zaxo (Archbishop) on Nov 17, 2002 at 22:11 UTC
Here you go: `my ($member,$total) = 'johndoe'; $total += $main{$_}{$member} for keys %main;` [download] If you want to do that for each member, it would be convenient to define a %total hash with member names as keys. It could go like this: `my %total; for my $month (keys %main) { $total{$_} += $main{$month}{$_} for keys %{$main{$month}}; }` [download] I think %main could use a better name. After Compline, Zaxo	[reply] [d/l] [select]
Re: HoH Issue(AKA Iterating over hash elements) by Enlil (Parson) on Nov 17, 2002 at 22:04 UTC
After perusing through the perldsc, you might come up with something like the following code (untested):`my $johndoe_hours = 0; foreach my $month ( keys %main } { $johndoe_hours += $johndoe_hours + $main{$month}{johndoe}; }` [download] `my $johndoe_hours = 0; foreach my $month ( keys %main } { $johndoe_hours += $main{$month}{johndoe}; }` [download] If you want to get rid of the error message when {johndoe} does not exist in the hash `$main{$month}` (that is assuming you are using warnings), you might want to do something like the following instead: `my $johndoe_hours = 0; foreach my $month ( keys %main } { if ( exists $main{$month}{johndoe} ) { $johndoe_hours += $johndoe_hours + $main{$month}{johndoe}; } }` [download] `my $johndoe_hours = 0; foreach my $month ( keys %main } { if ( exists $main{$month}{johndoe} ) { $johndoe_hours += $main{$month}{johndoe}; } }` [download] update: Fixed code from doubling johndoe's hours. -enlil	[reply] [d/l] [select]
Re: Iterating over hash elements by pg (Canon) on Nov 18, 2002 at 07:54 UTC
It makes more sense to use HoA in this case. Let hash key be the person's name, and value be the ref to an array, which has 12 elements, and each array element contains the hours for that month that person.	[reply]