问题
I have a dataframe, df, which has factor variable for date in the following format:
2015-12-15 10:00:00
2015-12-19 12:00:00
2015-12-20 20:00:00
It is hourly data. The problem arises when looking at midnight, 00:00:00, because it doesn't appear the hour. It just says:
21/12/2015
So as you see, it only says the day but it lacks the hour. So I use strptime to convert to a date format using:
df$date <- strptime(df$date,"%d/%m/%Y %H:%M")
It all works fine for all the hours and days except for any day at midnight, 00:00:00, which returns:
NA
I'd really appreciate some help as I've been looking at previous posts in StackOverflow and other forums but I havent' managed to figure out the solution for this specific problem yet.
回答1:
From R's strptime documentation (emphasis added):
format
A character string. The default for the format methods is "%Y-%m-%d %H:%M:%S" if any element has a time component which is not midnight, and "%Y-%m-%d" otherwise. If options("digits.secs") is set, up to the specified number of digits will be printed for seconds.
So the information is still there, you just need to format it to print it out with the time components.
> midnight <- strptime("2015-12-19 00:00:00","%Y-%m-%d %H:%M")
> midnight
[1] "2015-12-19 EST"
> format(midnight,"%Y/%m/%d %H:%M")
[1] "2015/12/19 00:00"
回答2:
If we have a vector like "v1", by using strptime we get NA for those elements that don't have the correct format
strptime(v1, "%d/%m/%Y %H:%M:%S", tz = "UTC")
#[1] "2015-12-19 12:00:00 UTC" NA
One way to correct this will be to paste the "00:00:00" string for those that doesn't have that
v1[!grepl(":", v1)] <- paste(v1[!grepl(":", v1)], "00:00:00")
strptime(v1, "%d/%m/%Y %H:%M:%S", tz = "UTC")
#[1] "2015-12-19 12:00:00 UTC" "2015-12-19 00:00:00 UTC"
Or if we use lubridate, the parse_date_time can take multiple formats
library(lubridate)
parse_date_time(v1, guess_formats(v1, c("%d/%m/%Y %H:%M:%S", "%d/%m/%Y")))
#[1] "2015-12-19 12:00:00 UTC" "2015-12-19 00:00:00 UTC"
data
v1 <- c("19/12/2015 12:00:00", "19/12/2015")
来源：https://stackoverflow.com/questions/37089536/how-can-i-keep-midnight-0000h-using-strptime-in-r