I recently came across dplyr and - as a newbie - like it very much. Hence, I try to convert some of my base-R code into dplyr-code.
Working with air traffic control data, I am struggling with coercing timestamps using lubridate and as.POSIXlt to parse timestamps embedded in a mutate_each() call. I need the POSIXlt format as I have to work with local times (at different locations) later on. Reading in the data delivers a data frame of characters. The following is a simplistic example:
ICAO_ADEP <- c("DGAA","ZSPD","UAAA","RJTT","KJFK","WSSS")
MVT_TIME_UTC <- c("01-Jan-2013 04:02:24", NA,"01-Jan-2013 04:08:18", NA,"01-Jan-2013 04:17:11","01-Jan-2013 04:21:52")
flights <- data.frame(ICAO_ADEP, MVT_TIME_UTC)
The function I wrote reads as follows:
make_POSIXlt <- function(vec, tz="UTC"){
vec <- parse_date_time(vec, orders="dmy_hms", tz=tz)
vec <- as.POSIXlt(vec, tz=tz)
}
The code works fine when executed with a single column:
flights$MVT_TIME_UTC <- make_POSIXlt(flights$MVT_TIME_UTC)
If I run the following dplyr code the function fails:
flights$BLOCK_TIME_UTC <- mutate_each(flights, funs(make_POSIXlt(.)), MVT_TIME_UTC)
Error: wrong result size (9), expected 6 or 1
The issue should be linked with the as.POSIXlt call. If this line is commented out the code works within mutate_each and coerces the timestamp into POSIXct.
Any idea/help on what is wrong? Obviously, my data has several timestamps that I would like to coerce with mutate_each (or any other suitable dplyr function) ...
Revisiting my question about 4 years later, I realised that I forgot to mark it as answered. However, this also gives me the chance to document how this (relatively) simple type coercion can (meanwhile) elegantly solved with dplyr
and lubridate
.
Key lesson learned:
- never use POSIXlt with a data frame (and its later brother tibble, although you can now work with list columns).
- coerce date-timestamps with the helpful parser functions from the
lubridate
package.
For the example from above
ICAO_ADEP <- c("DGAA","ZSPD","UAAA","RJTT","KJFK","WSSS")
MVT_TIME_UTC <- c("01-Jan-2013 04:02:24", NA,"01-Jan-2013 04:08:18", NA,"01-Jan-2013 04:17:11","01-Jan-2013 04:21:52")
flights <- data.frame(ICAO_ADEP, MVT_TIME_UTC)
flights <- flights %>% mutate(MVT_TIME_UTC = lubridate::dmy_hms(MVT_TIME_UTC)
will coerce the timestamps in MVT_TIME_UTC. Check the documentation on lubridate for other parsers and/or how to handle local time zones.
来源:https://stackoverflow.com/questions/27641129/dplyr-mutate-each-colswise-coercion-to-posixlt-fails