用R进行数据和时间转换

Question

I'm using R Studio. When I try to convert the date and time format using as.Date or as.Time I'm getting NA as the result. I also tried to set the Locale as it has been recommended in some of the problems in SO, that's also not helping. The default class is factor after I import from the text file. I also tried to make it a character. Still the problem exists. Any help?

> x<-c("16-12-2006")  
> class(x)
[1] "character"
> y<-as.Date(x)
> class(y)
[1] "Date"
> y<-as.Date(x,format="d%m%Y%")
> class(y)
[1] "Date"
> y
[1] NA

Answer 1

You are just misplacing the % s and missing the - s in your format string. The format string needs to match the string characters exactly (spaces, hyphens, commas, colons, etc.). See the document: Date-time Conversion Functions to and from Character .

Try:

> y <- as.Date(x, format="%d-%m-%Y") 

and it should work.

Answer 2

Try this:

> x <- as.POSIXct(strptime("11-09-2015", "%d-%m-%Y"))
> as.Date(x)
[1] "2015-09-10"
> x
[1] "2015-09-11 CEST"

x is a class of "POSIXct" and "POSIXt", but as.Date(x) is a class of "Date" and you can use it as x-axis in ggplot.