Re^7: Converting local time to utc time

I might need to code round this with the information I have. I only have a date/time (per minute) and a series of associated weather parameters, temp, wind etc.

These records come in sequence, as the local time changes, going from BST to GMT(UTC) or back the local time either repeats an hour or misses an hour. If I can detect this change (i.e. work out the day the clocks change) then I can probably build in the correct (duplicate/missing) times. The clock change always occurs during a given hour on variable days - it's always GMT/BST times in the source data.

I was hoping that this module would do this for me, but if not then I'll need to go away and think about how to build a solution. But, will need to think how I'm going to do it!

Comment on Re^7: Converting local time to utc time

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Re^8: Converting local time to utc time by poj (Abbot) on Nov 12, 2014 at 19:53 UTC
The change forward is not a problem, it's moving back that creates the ambiguity. As I see it you need to delay applying the UTC timezone until the second sequence of 01:00 to 01:59 times on the change day. I suggest using the `is_DST` method to detect the change, and a hash to remember when the time repeats. For example : #!perl use DateTime; use DateTime::TimeZone; use strict; my %seen=(); my $tz = 'UTC'; my $last; while (<DATA>){ chomp; next unless ($_); my ($y,$m,$d,$hr,$min) = split /\D/,$_; print "$_ : "; my $dt = DateTime->new ( year => $y, month => $m, day => $d, hour => $hr, minute => $min, time_zone => 'Europe/London', ); print $dt->is_dst," : "; if ($m==10 && $hr==1){ if ($dt->is_dst() ne $last){ $tz = '-1:00'; } $tz = 'UTC' if ++$seen{$min} > 1; } else { %seen=(); } $last = $dt->is_dst(); $dt->set_time_zone($tz); print $dt->strftime("%Y-%m-%d %H:%M")," $tz \n"; } __DATA__ 2014-03-30 00:59 2014-03-30 02:00 2014-03-30 02:01 2014-03-30 02:30 2014-03-30 02:59 2014-03-30 03:00 2014-03-30 03:01 2014-03-30 03:30 2014-03-30 03:59 2014-03-30 04:00 2014-03-30 04:01 2014-03-30 04:02 2014-10-26 00:59 2014-10-26 01:00 2014-10-26 01:01 2014-10-26 01:30 2014-10-26 01:59 2014-10-26 01:00 2014-10-26 01:01 2014-10-26 01:30 2014-10-26 01:59 2014-10-26 02:00 2014-10-26 02:01 2014-10-26 02:02 [download]	[reply] [d/l] [select]

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Re^8: Converting local time to utc time
by poj (Abbot) on Nov 12, 2014 at 19:53 UTC

The change forward is not a problem, it's moving back that creates the ambiguity. As I see it you need to delay applying the UTC timezone until the second sequence of 01:00 to 01:59 times on the change day. I suggest using the is_DST method to detect the change, and a hash to remember when the time repeats. For example :

#!perl
use DateTime;
use DateTime::TimeZone;
use strict;
my %seen=();
my $tz = 'UTC';
my $last;
while (<DATA>){
  chomp;
  next unless ($_);
  my ($y,$m,$d,$hr,$min) = split /\D/,$_;
  print "$_ : ";
  my $dt = DateTime->new (
    year   => $y, month  => $m,
    day    => $d, hour   => $hr,
    minute => $min,    
    time_zone => 'Europe/London',
  );
  
  print $dt->is_dst," : ";
  if ($m==10 && $hr==1){
    if ($dt->is_dst() ne $last){
      $tz = '-1:00';
    }
    $tz = 'UTC' if ++$seen{$min} > 1;
  } else {
    %seen=();
  }

  $last = $dt->is_dst();
  $dt->set_time_zone($tz);   
  print $dt->strftime("%Y-%m-%d %H:%M"),"  $tz \n";
}

__DATA__
2014-03-30 00:59
2014-03-30 02:00
2014-03-30 02:01
2014-03-30 02:30
2014-03-30 02:59
2014-03-30 03:00
2014-03-30 03:01
2014-03-30 03:30
2014-03-30 03:59
2014-03-30 04:00
2014-03-30 04:01
2014-03-30 04:02

2014-10-26 00:59
2014-10-26 01:00
2014-10-26 01:01
2014-10-26 01:30
2014-10-26 01:59
2014-10-26 01:00
2014-10-26 01:01
2014-10-26 01:30
2014-10-26 01:59
2014-10-26 02:00
2014-10-26 02:01
2014-10-26 02:02
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