MATLAB Central Newsreader - daylight savings adjustment

daylight savings adjustment

Steve — Wed, 01 Aug 2007 17:52:42 -0400

I have several years' worth of hourly data in Excel. Times are given and they take into account daylight saving. How can I locate all of the time data that is affected by daylight saving (as of 2007, it starts at 2:00 AM on the second Sunday in March and ends at 2:00 AM on the first Sunday in November) and subtract one hour from the values?

This one has stumped me for a while now. Any help is appreciated. Thanks!

Re: daylight savings adjustment

roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) — Wed, 01 Aug 2007 18:21:46 -0400

In article <f8qh9a$l69$1@fred.mathworks.com>,
Steve <steveDEL.bachmeierDEL@yahoo.com> wrote:
>I have several years' worth of hourly data in Excel. Times are given
>and they take into account daylight saving. How can I locate all of
>the time data that is affected by daylight saving (as of 2007, it
>starts at 2:00 AM on the second Sunday in March and ends at 2:00 AM on
>the first Sunday in November) and subtract one hour from the values?

How are the times encoded?

datenum and datevec might be of assistance.
--
"law -- it's a commodity"
-- Andrew Ryan (The Globe and Mail, 2005/11/26)

Re: daylight savings adjustment

Steve — Wed, 01 Aug 2007 18:45:25 -0400

The dates are in Excel as 'd/m/yyyy'. I transferred to Matlab and converted as follows:

------

[datanum datatxt dataraw]=xlsread('filename');

dates=datatxt(3:end,1); %These are of form 'd/m/yyyy'

tdst=cell2mat(dataraw(3:end,2))*24; %Converts times from form '3:00 PM' to form '15'

------

Now I need to take the 'tdst' values (daylight saving times) and subtract 1 - but only between the dates/times 2:00 AM on the second Sunday in March and 2:00 AM on the first Sunday in November. The problem is that these datenums change, and so I'm currently trying to hunt down the dates using something like

for time=t'
march{time}=calendar(year(time),3);
november{time}=calendar(year(time),11);
startDSTloc=march(find(min(march(:,1)>0))+1,1);
endDSTloc=november(find(min(november(:,1)>0)),1);
end

Then I'd somehow specifiy tstd=tdst-1 only for tdst between '3/march(startDSTloc,1)/year 2:00AM' and '11/november(endDSTloc,1)/year 2:00AM'.

Any suggestions? Thanks.

roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) wrote in message <f8qivq$dlm$1@canopus.cc.umanitoba.ca>...
> In article <f8qh9a$l69$1@fred.mathworks.com>,
> Steve <steveDEL.bachmeierDEL@yahoo.com> wrote:
> >I have several years' worth of hourly data in Excel. Times are given
> >and they take into account daylight saving. How can I locate all of
> >the time data that is affected by daylight saving (as of 2007, it
> >starts at 2:00 AM on the second Sunday in March and ends at 2:00 AM on
> >the first Sunday in November) and subtract one hour from the values?
>
> How are the times encoded?
>
> datenum and datevec might be of assistance.
> --
> "law -- it's a commodity"
> -- Andrew Ryan (The Globe and Mail, 2005/11/26)

Re: daylight savings adjustment

roberson@ibd.nrc-cnrc.gc.ca (Walter Roberson) — Wed, 01 Aug 2007 19:14:41 -0400

In article <f8qkc5$pka$1@fred.mathworks.com>,
Steve <steveDEL.bachmeierDEL@yahoo.com> wrote:

>Now I need to take the 'tdst' values (daylight saving times) and
>subtract 1 - but only between the dates/times 2:00 AM on the second
>Sunday in March and 2:00 AM on the first Sunday in November. The
>problem is that these datenums change, and so I'm currently trying to
hunt down the dates using something like

>for time=t'
>march{time}=calendar(year(time),3);
>november{time}=calendar(year(time),11);
>startDSTloc=march(find(min(march(:,1)>0))+1,1);
>endDSTloc=november(find(min(november(:,1)>0)),1);
>end

I'm not sure what t is here, and I suspect you want startDSTloc
and endDSTloc to be indexed by {time} . And since you are going
over multiple years, you need to take into account that the rules
changed this year.

>Then I'd somehow specifiy tstd=tdst-1 only for tdst between '3/march(startDSTloc,1)/year 2:00AM' and '11/november(endDSTloc,1)/year 2:00AM'.

Once you have figured out the appropriate start and stop times,
datenum() them, and then the positions that need to be changed
are the ones whose datenum() fall between the two values.
--
"law -- it's a commodity"
-- Andrew Ryan (The Globe and Mail, 2005/11/26)