Is there a way to check if a column is a Date in R?

Question

This is a pseudo followup to this question: Why is ggplot graphing null percentage data points?

Let's say this is my dataset:

Date        AE      AA      AEF     Percent 1/1/2012    1211    1000    3556    0.03 1/2/2012    100     2000    3221    0.43 1/3/2012    3423    10000   2343    0.54 1/4/2012    10000   3000    332     0.43 1/5/2012    2342    500     4435    0.43 1/6/2012    2342    800     2342    0.23 1/7/2012    2342    1500    1231    0.12 1/8/2012    111     2300    333  1/9/2012    1231    1313    3433     1/10/2012   3453    5654    222  1/11/2012   3453    3453    454  1/12/2012   5654    7685    3452   > str(data) 'data.frame':   12 obs. of  5 variables:  $ Date   : Factor w/ 12 levels "10/11/2012","10/12/2012",..: 1 2 3 4 5 6 7 8 9 10 ...  $ AE     : int  1211 100 3423 10000 2342 2342 2342 111 1231 3453 ...  $ AA     : int  1000 2000 10000 3000 500 800 1500 2300 1313 5654 ...  $ AEF    : int  3556 3221 2343 332 4435 2342 1231 333 3433 222 ...  $ Percent: num  0.03 0.43 0.54 0.43 0.43 0.23 0.12 NA NA NA ... 

I need something to tell that the 'Date' column is a Date type as opposed to a numeric or character type (this is because I have to convert the 'Date' column of the data input into an actual Date with as.Date(), ASSSUMING that I do not know the column names of the data set).

is.numeric(data[[1]]) returns False is.character(data[[1]]) returns False 

I made the 'Date' column in Excel, formatting the column in the 'Date' format, then saved the file as a csv. What type is this in R? I seek an expression similar to the above that returns TRUE.

Answer 1

Use inherits to detect if argument has datatype Date:

is.date <- function(x) inherits(x, 'Date')  sapply(list(as.Date('2000-01-01'), 123, 'ABC'), is.date) #[1]  TRUE FALSE FALSE 

If you want to check if character argument can be converted to Date then use this:

is.convertible.to.date <- function(x) !is.na(as.Date(as.character(x), tz = 'UTC', format = '%Y-%m-%d'))  sapply(list('2000-01-01', 123, 'ABC'), is.convertible.to.date) # [1]  TRUE FALSE FALSE 

Answer 2

You could try to coerce all the columns to as.Date and see which ones succeed. You would need to specify the format you expect dates to be in though. E.g.:

data <- data.frame(   Date=c("10/11/2012","10/12/2012"),   AE=c(1211,100),   Percent=c(0.03,0.43) )  sapply(data, function(x) !all(is.na(as.Date(as.character(x),format="%d/%m/%Y")))) #Date      AE Percent  #TRUE   FALSE   FALSE