comparing array to hashmap and deleting elements from hash in perl

Question

I have a file being read in then changed into an array then counted and put into a hash table. I then read in another file that has stop words into an array. I want to take the array of stop words and compare it to the hash table and if a word from the stop words is a match then it deletes it from the hash table.

I'm curious as to what methods I could do to achieve this using perl. I wont post my code, because I'm refraining from having other people write my code. I just would like to know how I could go about this. If someone has a good website I could reference that could help.

It's difficult if you don't post code, but you can at least explain what you tried. Personally, I would remove the stop words from the array, then make the hash. — gpojd
– gpojd, Commented Nov 19, 2012 at 14:58
@gpojd why would you prefer to do that? I can do that though. Just move the array to hash around. Is comparing an array to an array and deleting elements easier? — Kirs Kringle
– Kirs Kringle, Commented Nov 19, 2012 at 15:00

gpojd · Accepted Answer · 2012-11-20 13:17:41Z

3

Try this:

my %table = some_sub_to_populate_table();
my @stop_words = some_sub_to_get_stopwords();
for my $stop_word ( @stop_words ) {
    delete $table{ $stop_word };
}

edited Nov 20, 2012 at 13:17

answered Nov 19, 2012 at 15:08

gpojd

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1 Comment

Kirs Kringle Over a year ago

I'm going to try this, I asked someone else they said it would be easier to compare arrays to arrays, but I think it seems more logical to compare an array to a hash table and delete hashes instead of restricting an array every time.

pyr0 · Accepted Answer · 2012-11-19 15:14:50Z

1

this should work, too

open FH,"<".$PATH or die $!;
my $table={};
while(<FH>){
    $table->{$_}=VALUE
}
close FH;
open FH,"<".$PATH2 or die $!;
my @arr=<FH>;
close $FH;
delete $table{$_} foreach(@arr);

regards

answered Nov 19, 2012 at 15:14

pyr0

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2 Comments

dgw Over a year ago

You should use the three-argument-version of open together with lexical filehandles. So for example open my $fh, '<', $filename or die $!;

dgw Over a year ago

You are constructing a hashref and then try to delete key within a hash, you should be more exact in your example.

Carlisle18 · Accepted Answer · 2012-11-26 05:14:37Z

1

I would initially use the simple loop solution but am also interested on other ways to do it. Maybe you could try this one?

my %new_table = map { $_ => $old_table{$_} } grep { not $_ ~~ @stop_words } keys %old_table;

1: It gets all the hash keys not in @stop_words using grep:

grep { not $_ ~~ @stop_words } keys %old_table;

2: Using those keys, it creates a new hash using map:

my %new_table = map { $_ => $old_table{$_} }

If you will be transforming them into arrays, you could use array_minus of Array::Utils

edited Nov 26, 2012 at 5:14

answered Nov 20, 2012 at 10:39

Carlisle18

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