I need some help comparing two times in R. Currently I have a column of imported data formatted as HH:%M %p (e.g. 03:15 PM, not 3:15 PM). I need to create a new column and flag any row wherein the time is before 10:00 AM.
I have scoured the internet and stared forever at similar solutions, but can't seem to get it to work.
Any help would be appreciated! Thank you!
UPDATE
This is a clear update that shows a neat way of using data.table::as.ITime. It pretty much combines dickoa 's answer, Frank's comment and my answer for a best result.
library(data.table)
#example vector
vec <- c('09:00 PM', '11:00 PM', '09:00 AM')
#format can be used in the same way as in POSIXct
as.ITime(vec, format = "%I:%M %p") < as.ITime('10:00')
[1] FALSE FALSE TRUE
#notice that as.ITime does not create dates (alongside the times) as POSIX** does
#It only deals with times
#> as.ITime(vec, format = "%I:%M %p")
#[1] "21:00:00" "23:00:00" "09:00:00"
Or by using a data.table as per Frank's comment below:
ivec <- as.ITime(vec)
setDT(list(ivec))[, V1 := as.ITime(vec, "%I:%M %p")]
Original Answer
#using safe.ifelse to keep attributes
#function borrowed from here:
#http://stackoverflow.com/questions/6668963/how-to-prevent-ifelse-from-turning-date-objects-into-numeric-objects
safe.ifelse <- function(cond, yes, no){ class.y <- class(yes)
X <- ifelse(cond,yes,no)
class(X) <-class.y; return(X)}
library(data.table)
#example vec
vec <- c('09:00 PM', '11:00 PM', '09:00 AM')
#convert them to time using as.ITime from data.table and safe.ifelse
#basically I use safe.ifelse to detect PM in the vec
#if there is a PM then I convert that to an 24-hour time by adding 12 hours
new_vec <- safe.ifelse(grepl('PM', vec), as.ITime(vec) + 12*3600, as.ITime(vec))
> new_vec
[1] "21:00:00" "23:00:00" "09:00:00"
Finally comparing with 10:00 AM
> new_vec < as.ITime('10:00')
[1] FALSE FALSE TRUE
Or as mentioned by @Frank in the comments, since vec is a column in your data.frame this would probably be a better approach (and you wouldn't need to use safe.ifelse):
ivec <- as.ITime(vec)
setDT(list(ivec))[grepl('PM', vec), V1 := V1 + 12L*3600L ]
After seeing @dickoa 's answer, it seems that his answer with a format, works with as.ITime too:
vec <- c('09:00 PM', '11:00 PM', '09:00 AM')
> as.ITime(vec, "%I:%M %p")
[1] "21:00:00" "23:00:00" "09:00:00"
Which means that a simple:
ivec <- as.ITime(vec)
setDT(list(ivec))[, V1 := as.ITime(vec, "%I:%M %p")]
Would be enough. So, IMO a combination of our answers (and @Frank 's comment) would probably be the best solution (as.ITime will not create the dates that strptime does).
You can strptime to convert your times to POSIXlt and then compare it to your target time.
time <- c("11:20 AM", "03:15 AM", "09:20 PM", "12:23 AM", "10:01 AM")
target <- "10:00 AM"
strptime(time, "%I:%M %p") > strptime(target, "%I:%M %p")
## [1] TRUE FALSE TRUE FALSE TRUE
