R: Why Does Strptime Always Return Na When I Try to Format a Date String

R: Why does strptime always return NA when I try to format a date string?

strptime automatically runs as.character on the first argument (so it doesn't matter that it's a factor) and any trailing characters not specified in format= are ignored (so "EDT" doesn't matter).

The only issues are the typo @Ben Bolker identified (%m should be %d) and %H should be %I (?strptime says you should not use %H with %p).

# %b and %m are both *month* formats
strptime("Jul 05, 2011 09:30 PM EDT", "%b %m, %Y %H:%M %p", tz="")
# [1] NA

# change %m to %d and we no longer get NA, but the time is wrong (AM, not PM)
strptime("Jul 05, 2011 09:30 PM EDT", "%b %d, %Y %H:%M %p", tz="")
# [1] "2011-07-05 09:30:00"

# use %I (not %H) with %p
strptime("Jul 05, 2011 09:30 PM EDT", "%b %d, %Y %I:%M %p", tz="")
# [1] "2011-07-05 21:30:00"

NA while using strptime function

I find another thread which gives me a solution. Because my system language is not English, it cannot recognize "October". After I change it to "10", the code runs perfectly. Thanks for all the help.

as.Date returning NA while converting from 'ddmmmyyyy'

Works for me. The reasons it doesn't for you probably has to do with your system locale.

?as.Date has the following to say:

## This will give NA(s) in some locales; setting the C locale
## as in the commented lines will overcome this on most systems.
## lct <- Sys.getlocale("LC_TIME"); Sys.setlocale("LC_TIME", "C")
x <- c("1jan1960", "2jan1960", "31mar1960", "30jul1960")
z <- as.Date(x, "%d%b%Y")
## Sys.setlocale("LC_TIME", lct)

Worth a try.

No way to solve as.Date returning NA

The format should match the order, %m is for numeric months

as.Date(date, format="%d-%b-%Y")
#[1] "1994-11-23"

---

Also, this can be done with lubridate

library(lubridate)
dmy(date)
#[1] "1994-11-23"

Or with anytime

anytime::anydate(date)
#[1] "1994-11-23"

Changing date format (NA error)

You can use the correct format

df$date <- as.Date(df$date, format='%Y%m%d')

It is not clear whether you have numeric or non-numeric 'date' column. If it is 'numeric', convert to 'character' first

df$date <- as.Date(as.character(df$date), format='%Y%m%d')

But, strptime would work even if the column is numeric.

Or using library(lubridate)

library(lubridate)
ymd(df$date)

strptime not recognizing %b/%B?

I am a bit confused by R's behaviour in the case of missing values in strptime. The documentation is clear enough:

For strptime the input string need not specify the date completely: it
is assumed that unspecified seconds, minutes or hours are zero, and an
unspecified year, month or day is the current one. Some components may
be returned as NA (but an unknown tzone component is represented by an
empty string).

But that doesn't always seem to be the case with months. Here is a particularly odd example:

strptime('Nov-01', '%B-%d')
[1] "2014-11-01"
strptime('2009-Nov', '%Y-%B')
[1] NA

An obvious workaround based on the above would be to make a simple function.

convert.months <- function(x) 
     strptime(paste(x,strftime(Sys.time(),'%d')), '%b %d')

Which is ugly, but it works:

convert.months(c("Nov","Dec"))
[1] "2014-11-18 EST" "2014-12-18 EST"

---

To be clear here are the test cases, which, according to my interpretation of the documentation, should all work:

strptime('11', '%m') # Fail
strptime('11-01', '%m-%d') # Works
strptime('2009-11', '%Y-%m') # Fail

strptime('Nov', '%b') # Fail
strptime('Nov-01', '%b-%d') # Works
strptime('2009-Nov', '%Y-%b') # Fail

---

Related Topics