in reply to Re: Finding gaps in date ranges
in thread Finding gaps in date ranges

boohoo, the above article is mine, but I posted it anonymously by mistake. oh higher powers, if it please you, transfer the XPs of the article to this humble scribe.

I'm a big fan of peanos axioms. So I started with the idea: if it weren't dates we were dealing with, but natural numbers, then I would just sort the numbers, and compute the gaps with one simple loop. I decided to convert you date-format to something that can be sorted numerically (YYYYMM, with month in two digits, like "02"), and I made up a function "nextmonth" for incrementing the date.

sub nextmonth { my($year, $month); $year = substr($_[0], 0, 4); $month = substr($_[0], 4, 2); $month++; while ($month > 12) { $year++; $month-=12; } return $year . sprintf("%02d", $month); } sub find_gaps { my $dates = shift; my(@missing, @keys, $last); # convert your date-format to mine @keys = map { s/-(.)$/0$1/; s/-//; $_ } keys %$dates; # my format can be sorted numerically @keys = sort @keys; # in the loop we need two variables: # $last for the date before the current one, # and $date for the current date $last = shift(@keys); foreach my $date ( @keys ) { while (1) { $last = nextmonth($last); last if $last eq $date; push(@missing, $last); } $last = $date; } # convert my date-format back to yours @missing = map { s/0(.)$/$1/; s/^(....)/$1-/; $_ } @missing; return \@missing; }

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Brigitte    'I never met a chocolate I didnt like'    Jellinek