I thought that you had to specify a starting value for $hoh{$c1}{$c2}{count}.

When you dereference or modify a non-existing array or hash element, it will automatically "spring to life", including all the necessary intermediate hashes/arrays. For example:

my %test;
$test{a}[2]{b} = 'Hello';

# %test now contains:
#   ( a => [ undef,
#            undef,
#            { b => "Hello" } ] )

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It's called autovivification, and it's one of the nice features that make Perl special... :)   See Wikipedia and perlreftut for more info.

In addition, the ++ (auto-increment) operator silently treats undef as 0. So you don't need to specify an initial value.


what if I wanted to start that count at 5?

One solution would be to create the hash first, and then use another loop to add 5 to each counter.

Alternatively, you can do a check inside the loop (before incrementing!) to see if the counter has already been incremented previously, and if not, initialize it with the number 5:

if (!$hoh{$c1}{count}) { $hoh{$c1}{count} = 5; }   # verbose form

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$hoh{$c1}{count} ||= 5;   # shortcut

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(See C style Logical Or and Assignment Operators.)

In reply to Re^3: Count number of elements in HoH and sum them for other keys by smls
in thread Count number of elements in HoH and sum them for other keys by Sosi

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