in reply to Re: Using array value (from array ref) as hash key??
in thread Using array value (from array ref) as hash key??

Thanks for the reply and the clarification, I understand what you're saying now. :)

I remembered something I had problems with before and tried that and now I'm even more puzzled...(I've had problems with things not working due to whitespace issues so I fairly routinely use a trim function I got from the cookbook), I tried it with this problem and lo and behold it works.

my $months = $dbh->selectall_arrayref("select to_char(last_day(add_mon
+ths('14-May-2004', (rownum-1))),'MON-RRRR')  dt
from all_objects
where rownum <= months_between(sysdate,'31-May-2004')+1");

my $month;
my $monthhash;
my $i = 0;
# populate month hash with zero's for now (this may need to be done la
+ter)
foreach $month (@$months) {
    $monthhash{@$month[0]} = $i;
#    print "pop @$month[0] $i\n";
    $i++;
}

for($i=0; $i<$#$months; $i++) {
    print "hope 1 @{$months->[$i]}\n";
    print "hope 2 $monthhash{trim(@{$months->[$i]})}\n";
    print "hope 2A $monthhash{@{$months->[$i]}}\n";
}

sub trim {
    my @out = @_;
    for (@out) {
        s/^\s+//;        #trim left
        s/\s+$//;        #trim right
        }
    return @out == 1
        ? $out[0]        #only one to return
        : @out;            #or many
}

[download]

Results. I added an incrementing value to the hash when I created it to make sure that I was indeed getting the correct value - As far as I can see the only difference between hope 2 & hope 2A is the trim call, yet one works and the other doesn't. I don't know why this should make any difference but it is now working.

I was wondering whether it had anything to do with the array only having one element. I started with the simple query so I'll be using your notation later on. If thats not it, then I have no idea why the trim should make any difference.

hope 1 MAY-2004
hope 2 0
hope 2A
hope 1 JUN-2004
hope 2 1
hope 2A
hope 1 JUL-2004
hope 2 2
hope 2A
hope 1 AUG-2004
hope 2 3
hope 2A
hope 1 SEP-2004
hope 2 4
hope 2A

[download]

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Re^3: Using array value (from array ref) as hash key??
by ikegami (Patriarch) on May 25, 2007 at 06:08 UTC 
    $key = @...[...];    <--- Wrong
^      ^                  It may work because Perl is "smart",
|      |                  but Perl doesn't always guess correctly.
+------+

$key = $...[...];    <--- Right
^      ^
|      |
+------+

    [download]

    A hash key is a scalar, so you need a "$ expression". 

    # Wrong:
print "hope 1 @{$months->[$i]}\n";
print "hope 2 $monthhash{trim(@{$months->[$i]})}\n";
print "hope 2A $monthhash{@{$months->[$i]}}\n";

# Right:
print "hope 1 $months->[$i][0]\n";
print "hope 2 $monthhash{trim($months->[$i][0])}\n";
print "hope 2A $monthhash{$months->[$i][0]}\n";

    [download]

    You're assuming an array of one element (@array) is interchangeable with the element ($array[0]). That's not always the case. In fact, you should assume it's not the case.

    By the way, @out == 1 is a bug. You should replace @out == 1 with wantarray. You'll get some interesting results when you do.

[reply]
[d/l]
[select]

      Thanks for your patience Ikegami, I get it now. (finally) :)

      Thanks for the clarification about @out == 1 is a bug, I got that straight from the perl cookbook as a solution (1.19). But I can see that wantarray would be better.

[reply]

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