Timestamp editing help

[smithosaurus]

Hi,

I have a column of data in my data set which is a datestamp, looking like this:

2012-05-29 06:56:18

This is in one column, but I need to sort and analyze the data based on the time of day, and not the day of the year.

Is there a simple way to separate these values into two different columns?

[Lazar]

This is really clunky but it works:

#Fake data frame
data <- as.data.frame(rep("2012-05-29 06:56:18", 100))
#Making a new column in data frame with just time
data[,2]<- unlist(strsplit(as.character(data[,1]), " "))[c(F,T)]

This is ugly code and I am sure someone with knowledge of manipulating dates in R will give a much better answer.

[Jake]

Check out the 'lubridate' package.

[Lazar]

Jake the lubricate package seems to have functions for extracting hour(x),minute(x),second(x) but nothing for time. Is this right? The closest I could get was

library(lubridate)
x <- ymd_hms(rep("2012-05-29 06:56:18", 100))
paste(hour(x),minute(x),second(x), sep=":")

[Jake]

The goal is to sort the dates by time of day, right? How about this:

> x <- ymd_hms(rep("2012-05-29 06:56:18", 10))
Using date format %Y-%m-%d.
> hour(x) <- round(runif(10, 0, 23))
> minute(x) <- round(runif(10, 0, 59))
> second(x) <- round(runif(10, 0, 59))
> # in random order
> x
 [1] "2012-05-29 19:09:20 UTC" "2012-05-29 07:00:44 UTC"
 [3] "2012-05-29 16:22:34 UTC" "2012-05-29 03:59:54 UTC"
 [5] "2012-05-29 06:19:14 UTC" "2012-05-29 13:14:15 UTC"
 [7] "2012-05-29 05:27:44 UTC" "2012-05-29 06:25:33 UTC"
 [9] "2012-05-29 21:49:07 UTC" "2012-05-29 22:24:14 UTC"
> 
> # sort by time of day
> x[order(second(x) + 60*minute(x) + 60*60*hour(x))]
 [1] "2012-05-29 03:59:54 UTC" "2012-05-29 05:27:44 UTC"
 [3] "2012-05-29 06:19:14 UTC" "2012-05-29 06:25:33 UTC"
 [5] "2012-05-29 07:00:44 UTC" "2012-05-29 13:14:15 UTC"
 [7] "2012-05-29 16:22:34 UTC" "2012-05-29 19:09:20 UTC"
 [9] "2012-05-29 21:49:07 UTC" "2012-05-29 22:24:14 UTC"

[Lazar]

That works or even more simply:

 x[order(as.numeric(x - as.Date(x)))]

[Jake]

Clever approach. Although it's a little annoying that, at least for me, it throws a warning message :\