perl delete hash items if not found in an array

Question

I have the following hash: %{$data{$id}{$date}} that includes a large number of dates

and an array @dates that includes a subsection of dates found in the %hash.

What is the best way to loop through my %hash and delete all dates that are not found in @dates array? Once this is done I'd like the %hash to only have the values from @array dates.

I've tried 'delete unless exists' looking at keys after I created a hash from my @dates array but would get missing arguments error.

Please edit and show us the actual code you wrote that includes delete unless exists and the exact error message. — simbabque
– simbabque, Commented Jun 27, 2018 at 16:54

blhsing · Accepted Answer · 2018-06-27 22:00:43Z

4

You should loop through the keys of %{$data{$id}} instead.

my %dates = map {$_ => 1} @dates;
exists $dates{$_} or delete $data{$id}{$_} for keys %{$data{$id}};

edited Jun 27, 2018 at 22:00

answered Jun 27, 2018 at 16:34

blhsing

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Comments

Borodin · Accepted Answer · 2018-06-27 16:52:45Z

3

As long as the dates in @dates are guaranteed to appear in the hash you can use map

%{ $data{$id} } = map { $_ => $data{$id}{$_} } @dates

answered Jun 27, 2018 at 16:52

Borodin

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5 Comments

blhsing Over a year ago

Good alternative. $data is a reference to a hash so you need to write $$data{$id}{$_} instead of $data{$id}{$_}.

Borodin Over a year ago

@blhsing: If $data is a hash reference then the OP's code is wrong, and I have no reason to assume so.

Borodin Over a year ago

@blhsing: Even if you were correct, it would be best to write $data->{$id}{$_}

lalala53__ Over a year ago

@borodin Thanks! This filtered out all the correct dates but I end up with undef hash for all but the last date. I'll work on debugging this.

Borodin Over a year ago

You don't describe your data structure very carefull and I may have misunderstood it. If you add a dump of your hash into the question then it will help.

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