DST is a b!tch, be careful with POSIX in a stupid timezone
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At the department we have been analyzing some transaction data for some time. We got a new dataset with lots of transactions. Once you need interpurchase (IPT) times, posix is quite useful, as you can easily difference transactions to generate IPTs.Want to share your content on R-bloggers? click here if you have a blog, or here if you don't.
So the data is on a daily basis. However, some IPTs appeared to be decimal:
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date1 = strptime("2007/10/01","%Y/%m/%d") | |
date2 = strptime("2007/10/31","%Y/%m/%d") | |
difftime(date1,date2,units="days") | |
#Time difference of 30.04167 days | |
30.04167 days?? Well, of course R is right. So what’s the reason? Marco (thx!) quickly gave me hint: daylight savings time. In my timezone there is daylight savings time. By defaukt strptime() uses the current time zone. Switching to UTC solved the issue.
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date1 = strptime(20071001,"%Y%m%d",tz="UTC") | |
date2 = strptime(20071031,"%Y%m%d",tz="UTC") | |
diff(c(date1,date2),units="days",tz="UTC") | |
#Time difference of 30 days |
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