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Problem creating data.table with date-time column:

> mdt <- data.table(id=1:3, d=strptime(c("06:02:36", "06:02:48", "07:03:12"), "%H:%M:%S"))
> class(mdt)
[1] "data.table" "data.frame"
> print(mdt)
Error in `rownames<-`(`*tmp*`, value = paste(format(rn, right = TRUE),  : 
  length of 'dimnames' [1] not equal to array extent

Enter a frame number, or 0 to exit   

1: print(list(id = 1:3, d = list(sec = c(36, 48, 12), min = c(2, 2, 3), hour = c(6, 6, 7), mday = c(31,
2: print.data.table(list(id = 1:3, d = list(sec = c(36, 48, 12), min = c(2, 2, 3), hour = c(6, 6, 7), m
3: `rownames<-`(`*tmp*`, value = paste(format(rn, right = TRUE), ":", sep = ""))

Create as data.frame and convert to data.table works!

> mdf <- data.frame(id=1:3, d=strptime(c("06:02:36", "06:02:48", "07:03:12"), "%H:%M:%S"))
> print(mdf)
  id                   d
1  1 2014-01-31 06:02:36
2  2 2014-01-31 06:02:48
3  3 2014-01-31 07:03:12
> mdt <- as.data.table(mdf)
> print(mdt)
   id                   d
1:  1 2014-01-31 06:02:36
2:  2 2014-01-31 06:02:48
3:  3 2014-01-31 07:03:12
> class(mdt)
[1] "data.table" "data.frame"

Am I missing anything or is it bug? If a bug, where do I report it?

Note I use R version 3.0.0 and I see some warnings re. packages built with version 3.0.2. Can it be the problem? Should I upgrade R itself? Everything else I do seems to be working though.

Patrick
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  • possible duplicate of [cast string to IDateTime](http://stackoverflow.com/questions/14056370/cast-string-to-idatetime) – Blue Magister Jan 31 '14 at 18:43
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    [tag:data.table] does not support `POSIXlt` due to size and structure. Use `POSIXct` or `ITime` instead. Upgrade R to the latest version - generally it makes your life easier. – Blue Magister Jan 31 '14 at 18:44

1 Answers1

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Formatting response from Blue Magister's comment (thanks so much), data.table does not support POSIXlt data types for performance reason -- see cast string to IDateTime as suggested as possible duplicate.

So the way to go is to cast time as ITime (type provided by data.table) or date-time (or date only) as POSIXct, depending upon whether date info is important or not:

> mdt <- data.table(id=1:3, d=as.ITime(strptime(c("06:02:36", "06:02:48", "07:03:12"), "%H:%M:%S")))
> print(mdt)
   id        d
1:  1 06:02:36
2:  2 06:02:48
3:  3 07:03:12
> mdt <- data.table(id=1:3, d=as.POSIXct(strptime(c("06:02:36", "06:02:48", "07:03:12"), "%H:%M:%S")))
> print(mdt)
   id                   d
1:  1 2014-01-31 06:02:36
2:  2 2014-01-31 06:02:48
3:  3 2014-01-31 07:03:12

As an extra note in case someone can benefit from it, I wanted to create date & time from my input data with date & time in separate fields. I found it useful to learn (see ?ITime) that one can add time ITime to date-time POSIXct and get a date-time POSIXct as follows:

> mdt <- as.POSIXct("2014-01-31") + as.ITime("06:02:36")
> print(mdt)
[1] "2014-01-31 06:02:36 EST"
> class(mdt)
[1] "POSIXct" "POSIXt"
Community
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Patrick
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