On Mar 24, 2011, at 9:29 AM, Michael Bach wrote:
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?
I'm not sure what problem is odccuring with your method. The way I
would have done it worked. The findInterval function also seemed to
allow classification by intervals of 3600 seconds:
> subset(dfx, dx > as.POSIXct("2007-06-01 10:00:00") & dx <
as.POSIXct("2007-06-01 14:00:00"))
dx
41 2007-06-01 10:15:00
42 2007-06-01 10:30:00
43 2007-06-01 10:45:00
44 2007-06-01 11:00:00
45 2007-06-01 11:15:00
46 2007-06-01 11:30:00
47 2007-06-01 11:45:00
48 2007-06-01 12:00:00
49 2007-06-01 12:15:00
50 2007-06-01 12:30:00
51 2007-06-01 12:45:00
52 2007-06-01 13:00:00
53 2007-06-01 13:15:00
54 2007-06-01 13:30:00
55 2007-06-01 13:45:00
> findInterval(dfx$dx, c( as.numeric(range(dfx$dx)[1]
+(1:24)*3600) ) )
[1] 0 0 0 0 1 1 1 1 2 2 2 2 3 3 3 3 4 4 4 4 5
5 5 5 6 6 6 6 7
[30] 7 7 7 8 8 8 8 9 9 9 9 10 10 10 10 11 11 11 11 12 12
12 12 13 13 13 13 14 14
[59] 14 14 15 15 15 15 16 16 16 16 17 17 17 17 18 18 18 18 19 19 19
19 20 20 20 20 21 21 21
[88] 21 22 22 22 22 23 23 23 23 24 24 24 24
Best Regards,
Michael Bach
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