Re^2: pre-size a two-dimensional array

Hi ikegami,

Thank you. After reading your post my decision is to not pre-allocate the array and I have decided on using an array of hashes.

In the loop section where I am using the array and hash could you tell me if the hash 'dayHash' filled and pushed onto the @summary array for $wk=0 is different than the 'dayHash' pushed onto the @summary array for $wk=1? Said differently, am I saving a copy of the hash keys and values into the array or am I saving the same reference to the same hash in every element of the array and overwriting the hash values each time with the next week's order totals from %total_opd?

Thanks.

# create data for small summary table of all retailers

my $numWks = (($num_days - ( 7 - $firstDOW_curMonth )) / 7 ) + 1;
if ( (($num_days - ( 7 - $firstDOW_curMonth )) % 7 ) ) { $numWks++; }

my %dayHash;    # the hash
my @summary;     # the array of hashes

# init the blank portion of $summary[][] if there is one
#my $temp = 0;
#while ( $temp < $firstDOW_curMonth ) {
#    $summary[0][$temp++]
#}

my $wktotal;
my $count=1;  # key into %total_opd, it is based on date (1-$numdays)
my $firstDOW = $firstDOW_curMonth;

# $wk is index for array
for ( my $wk = 0; $wk < $numwks; $wk++ ) {
    $wktotal = 0;
    # the first time through $dw may be 0, 1, 2,...6
    # $dw is the key of the hash
    for ( my $dw = $firstDOW; $dw < 7; $dw++ ) {
        $dayHash{$dw} = $total_opd{$count};
        $wktotal += $total_opd{$count};
        last if ($count++ == $num_days);
    }
    $firstDOW = 0;    # next time through the $dw loop it will start a
+t 0
    $dayHash{7} = $wktotal;    # save the accumulated total for the we
+ek
    push @summary, $dayHash;    # 
    last if ($count > num_days);
}
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Re^3: pre-size a two-dimensional array by GrandFather (Saint) on Jul 12, 2007 at 04:23 UTC
I strongly recommend that you use strictures (`use strict; use warnings;`). That would pick up the use of `$numwks` and `$numWks` for example. It would also alert you to the use of the (presumably) undeclared `$dayHash` in `push @summary, $dayHash;` - although I suspect you really intended `push @summary, \%dayHash;`. Strictures would also alert you to the use of `num_days` in `last if ( $count > num_days );` which seems pretty unlikely given you've used `$num_days` a few lines up In answer to your actual question: yes, you will be pushing copies of the reference. The easy fix is to make `%dayHash` (and `$wktotal` btw) local to the loop: `for ( my $wk = 0 ; $wk < $numWks ; $wk++ ) { my $wktotal = 0; my %dayHash; ... }` [download] I notice that `$wk` is not used. You could just `for (1 .. $numWks) {` and if you do need it at some point you should `for my $wk (1 .. $numWks) {`. DWIM is Perl's answer to Gödel	[reply] [d/l] [select]
Re^3: pre-size a two-dimensional array by chrism01 (Friar) on Jul 12, 2007 at 04:16 UTC
You should push an anonymous hashref to get a new copy: push @summary, { %dayhash }; Cheers Chris	[reply]