[R] subset and as.POSIXct / as.POSIXlt oddness

From: Michael Bach <phaebz_at_gmail.com>
Date: Thu, 24 Mar 2011 15:29:15 +0200

Dear R users,

Given this data:

x <- seq(1,100,1)
dx <- as.POSIXct(x*900, origin="2007-06-01 00:00:00") dfx <- data.frame(dx)

Now to play around for example:

subset(dfx, dx > as.POSIXct("2007-06-01 16:00:00"))

Ok. Now for some reason I want to extract the datapoints between hours 10:00:00 and 14:00:00, so I thought well:

subset(dfx, dx > as.POSIXct("2007-06-01 16:00:00"), 14 > as.POSIXlt(dx)$hour & as.POSIXlt(dx)$hour < 10)
Error in as.POSIXlt.numeric(dx) : 'origin' must be supplied

Well that did not work. But why does the following work?

14 > as.POSIXlt(dx)$hour & as.POSIXlt(dx)$hour < 10

Is there something I miss about subset()? Or is there even another way of aggregating over an hourly time interval in a nicer way?

Best Regards,
Michael Bach

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