CODEWITHSUNDEEP
rdatetimedatetime-formatposixctposixlt
Rodrigo
Rodrigo

Reputation: 5119

In R, do as.POSIXlt and strptime require different formats?

Consider the following R console output.

> Sys.getlocale()
[1] "LC_CTYPE=en_US.UTF-8;LC_NUMERIC=C;LC_TIME=en_US.UTF-8;LC_COLLATE=en_US.UTF-8;LC_MONETARY=en_US.UTF-8;LC_MESSAGES=en_US.UTF-8;LC_PAPER=en_US.UTF-8;LC_NAME=C;LC_ADDRESS=C;LC_TELEPHONE=C;LC_MEASUREMENT=en_US.UTF-8;LC_IDENTIFICATION=C"
> dh <- '2018-05-08 07:42:34 PM'
> as.POSIXlt(dh,'%Y-%m-%d %I:%M:%S %p')
[1] "2018-05-08 07:42:34"
> strptime(dh,'%Y-%m-%d %I:%M:%S %p')
[1] "2018-05-08 19:42:34 -03"

If both formats are identical, why doesn't as.POSIXlt recognize the 12-hour format properly? dh gives a time at night (7 PM), but the function is returning a time in the morning! as.POSIXct gives the same error.

What am I missing here?

Upvotes: 1

Views: 35

Answers (1)

MKR
MKR

Reputation: 20085

The actual mistake seems to be in the line;

as.POSIXlt(dh, '%Y-%m-%d %I:%M:%S %p')

It should be as:

as.POSIXlt(dh, format= '%Y-%m-%d %I:%M:%S %p')
#[1] "2018-05-08 19:42:34 BST"

The 2nd argument for strptime is format. Hence, strptime(dh,'%Y-%m-%d %I:%M:%S %p') works fine as it considers 2nd argument as format.

But 2nd argument for as.POSIXlt is tz. Hence, the text provided to be considered as format is taken up as tz and default format is used. That was resulting in unexpected value.

Upvotes: 2

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