I'm trying to use Perl's DateTime
to subtract one day from another with a sign. I can get the days in between easily:
sub delta_days {
my $date1 = shift;
my $date2 = shift;
my $d1 = str_to_date_object($date1);
my $d2 = str_to_date_object($date2);
return $d2->delta_days($d1)->delta_days();
}
say delta_days('2021-10-21', '1980-8-20');
say delta_days('1980-8-20', '2021-10-21');
but both of these calls give the difference as 15037
, without a sign.
Following the documentation https://metacpan.org/pod/DateTime
I see
# not DST
my $dt1 = DateTime->new(
year => 2003,
month => 5,
day => 6,
time_zone => 'America/Chicago',
);
# is DST
my $dt2 = DateTime->new(
year => 2003,
month => 11,
day => 6,
time_zone => 'America/Chicago',
);
my $dur = $dt2->subtract_datetime($dt1)->days();
I have checked a similar question in How to make DateTime::Duration output only in days? but I don't see how to get a signed difference there.
How can I get the difference in days with a sign?
CodePudding user response:
Two issues: You're doing the subtraction on dates in the wrong order if you want a negative offset, and with the dates you're testing subtract_datetime()
with, the duration object is going to have 0 days.
Compare with this version:
#!/usr/bin/env perl
use strict;
use warnings;
use feature qw/say/;
use DateTime;
use Data::Dumper;
# not DST
my $dt1 = DateTime->new(
year => 2003,
month => 5,
day => 6,
time_zone => 'America/Chicago',
);
# is DST
my $dt2 = DateTime->new(
year => 2003,
month => 11,
day => 6,
time_zone => 'America/Chicago',
);
say $dt1;
say $dt2;
my $dur = $dt1->subtract_datetime($dt2);
print Dumper({$dur->deltas});
which when run produces
2003-05-06T00:00:00
2003-11-06T00:00:00
$VAR1 = {
'minutes' => 0,
'nanoseconds' => 0,
'months' => -6,
'seconds' => 0,
'days' => 0
};
Note the -6 months offset. DateTime::Duration
objects will not convert between months and days according to the documentation so this looks like a dead end.
The delta_days
method you looked at first returns the actual difference in days, but as noted it's an absolute value. You can add a check to convert it to negative if the first date is before the second:
my $days = $dt1->delta_days($dt2)->in_units('days');
$days *= -1 if $dt1 < $dt2;
say $days; # Prints -184
and a variation of your delta_days()
function:
sub delta_days {
my $date1 = shift;
my $date2 = shift;
my $d1 = str_to_date_object($date1);
my $d2 = str_to_date_object($date2);
return $d1->delta_days($d2)->in_units('days') * ($d1 < $d2 ? -1 : 1);
}
say delta_days('2021-10-21', '1980-8-20');
say delta_days('1980-8-20', '2021-10-21');