Efficiently convert a date column in data.table

Question

I have a large data set with many columns containing dates in two different formats:

\"1996-01-04\" \"1996-01-05\" \"1996-01-08\" \"1996-01-09\" \"1996-01-10         


        

Answer 1

Since you know beforehand there are only two date formats, this is easy. The format argument to as.Date is vectorized:

as_date_either <- function(x) {
    format_vec <- rep_len("%Y-%m-%d", length(x))
    format_vec[grep("/", x, fixed = TRUE)] <- "%m/%d/%Y"
    as.Date(x, format = format_vec)
}

Edited: replaced ifelse with subset assignment, which is faster