Good observations and thanks! In fact I need it once to be created and then I will access it many times. so this one time processing for me takes lots of time however it's important to be accessed later easily and not very time consuming. I can have a big memory of 50 GB but still is not enough and it goes out of memory! I tried to create the hash and then tie it, it would not also possible for me or maybe I do some errors that it still goes out of memory! 
my $t = tie(%hash, Tie::IxHash);
foreach my $line (@file){
    $line_count++;
    my @ngrams=produce_ngrams($line);
    foreach my $ngram (@ngrams) {
        #$t->Push(@{ $hash{$ngram} } => $line_count); 
        push(@{ $hash{$ngram} }, $line_count);
    }
}

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I have also no idea if I tie the hash, later on how can I access it from my hard drive.

In reply to Re^2: a large text file into hash by perl_lover_always
in thread Reaped: a large text file into hash by NodeReaper

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