Question about map function [ANSWERED]

automandc has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I have a subroutine that sorts a passed array. The array elements are hash references resulting from a "selectall_arrayref" DBI query against a SQL db. The sort routine selects the sort method (via separate subs) based on input flags. One of the fields I sort with is a "date" field where the dates come in the format "YYYY.MM.DD". I want to numerically sort these, which requires stripping the periods before passing into the sort. Here is what I have now:

sub sort_records {

    my $sort_routine;
    ($opt_g =~ /^t/i) ?    #flag setting sort order
        ($sort_routine = \&sort_by_title) :
        ($sort_routine = \&sort_by_date);
        
    foreach (@_) {  
        ($_->{'cleandate'} = $_->{'date'}) =~ s/\D//g;
    }      #do I need this?

    my @records =    map  { $_->[0] }
                    sort $sort_routine
                    map  { [ $_, $_->{'title'}, $_->{'cleandate'} ] } 
                     # or can I do it here?
                @_;
                
    return @records;
}
[download]

(The sort_by_title and sort_by_date subs are basic sort functions straight from the perl cookbook. Only difference is the order in which they compare the fields).

So my question is, can I get rid of the "foreach" loop and somehow do the same thing right in the map, but without changing the values in the source?

(Any other critiques/suggestions also welcome).

Comment on Question about map function [ANSWERED] Download Code

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Re: Question about map function [ANSWERED] by ikegami (Patriarch) on Nov 17, 2008 at 22:17 UTC
Why are you doing `my @records = map { $_->[0] } sort $sort_routine map { [ $_, $_->{'title'}, $_->{'cleandate'} ] } @_;` [download] instead of `my @records = sort $sort_routine @_;` [download] You're slowing things down and wasting memory. Also, `($opt_g =~ /^t/i) ? #flag setting sort order ($sort_routine = \&sort_by_title) : ($sort_routine = \&sort_by_date);` [download] is a complicated way of doing `$sort_routine = ( $opt_g =~ /^t/i ? \&sort_by_title : \&sort_by_date );` [download] I've never seen a situation where it made sense to use an assignment inside of the conditional operator (`?:`). So, if your date format is really YYYY.MM.DD (and not YYYY.M.D), you get `sub sort_records { my $sort_routine ( $opt_g =~ /^t/i ? sub { $a->{title} cmp $b->{title} } : sub { $a->{date} cmp $b->{date} } ); return sort $sort_routine @_; }` [download]	[reply] [d/l] [select]
Re^2: Question about map function [ANSWERED] by automandc (Acolyte) on Nov 19, 2008 at 03:13 UTC
Thanks, this is all very helpful. My perl is very rusty, but slowly coming back. I had just figured out the silliness of doing assignment inside the conditional, and could have saved myself a headache if I had read your response first! My sub routines actually had alternative sorts, so they checked the first choice (title or date) and then the second one. I have also now figured out (again, the hard way) that regular string comparison works fine for my date format (not sure why I thought differently). Sigh, live and learn. But my code is getting better.	[reply]
Re: Question about map function by ccn (Vicar) on Nov 17, 2008 at 19:45 UTC
You can perfectly sort "YYYY.MM.DD" values as strings with `cmp`. You don't need to strip dots. So the `foreach` loop doesn't needed at all. Update: but if you want numeric than `my @records = map { $_->[0] } sort $sort_routine map { $_->{'date'} =~ /(\d+)\.(\d+)\.(\d+)/; [ $_ +, $_->{'title'}, $1.$2.$3 ] }` [download] or shorter: `my @records = map { $_->[0] } sort $sort_routine map { [ $_, $_->{title}, join '', $_->{date} =~ /\d+/g ] }` [download]	[reply] [d/l] [select]
Re: Question about map function [SOLVED!] by automandc (Acolyte) on Nov 17, 2008 at 20:13 UTC
Perfect! I do want to sort numerically, hence the need to remove the periods. I tried your second (shorter) solution and it works exactly as needed. I knew there was a way to do it with regexes, but needed superior wisdom to show me the way. Much thanks.	[reply]
Re^2: Question about map function [SOLVED!] by runrig (Abbot) on Nov 17, 2008 at 20:36 UTC
If your months/days are 2-digit zero padded (as YYYY.MM.DD would indicate), then you don't need to sort numerically...alphabetically sorting is fine. Is the format, e.g., "2008.01.01" or "2008.1.1" ??	[reply]