CODEWITHSUNDEEP
rdatetime
user862507
user862507

Reputation: 85

Create a POSIXlt from a list of time components

I'm reading some JSON data into R, and it stores datetime information as separate time components (year, month, hour, etc.). Given that I already have the separate pieces, it seems like it should be easy to create a POSIXlt object, given that the latter is just a list of time components.

as.POSIXlt won't accept a named list or vector of components. It is possible to create a POSIXlt by adding the appropriate class and attr to a list, but it fails without the wday and yday elements, which I don't have.

I'm aware that I can convert the list to a string and parse it, but that's so inelegant a solution I thought I'd make sure there wasn't a better way.

Edit: ISOdatetime is exactly what I was looking for. Thanks!

Upvotes: 0

Views: 96

Answers (2)

IRTFM
IRTFM

Reputation: 263362

The ISOdate or ISOdatetime functions are clearly the ones to use but since you asked how to do it with POSIXlt as a starting point here's a bit of hacking:

 test <- as.POSIXlt("1970-01-01")
 dput(test)
structure(list(sec = 0, min = 0L, hour = 0L, mday = 1L, mon = 0L, 
    year = 70L, wday = 4L, yday = 0L, isdst = 0L, zone = "PST", 
    gmtoff = NA_integer_), .Names = c("sec", "min", "hour", "mday", 
"mon", "year", "wday", "yday", "isdst", "zone", "gmtoff"), class = c("POSIXlt", 
"POSIXt"))
 test$year <- 1941
 test$mon <- 12
 test$mday <-7
 test
#[1] "3842-01-07 PST"   Wrong offset
 test$year <- 41
 test
#[1] "1942-01-07 PST"    "An infamous date"

I suspect this is "wrong". in that I doubt the day of the week or other list items get properly rejiggered.

Upvotes: 0

Dave2e
Dave2e

Reputation: 24079

ISOdate is the command to use:

ISOdate(year, month, day, hour = 12, min = 0, sec = 0, tz = "GMT")

The function returns a POSIXct type. See ?ISOdate for more info.

Upvotes: 1

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