How to display real dates in a loop in r

Question

When I iterate over dates in a loop, R prints out the numeric coding of the dates.

For example:

dates <- as.Date(c(\"1939-06-10\", \"1932-02-22\"         


        

Answer 1

When you use dates as seq in a for loop in R, it loses its attributes.

You can use as.vector to strip attributes and see for yourself (or dput to see under the hood on the full object):

as.vector(dates)
# [1] -11163 -13828   3724   6284   6678   3526   8232   7284
dput(dates)
# structure(c(-11163, -13828, 3724, 6284, 6678, 3526, 8232, 7284), class = "Date")

In R, Date objects are just numeric vectors with class Date (class is an attribute).

Hence you're seeing numbers (FWIW, these numbers count days since 1970-01-01).

To restore the Date attribute, you can use the .Date function:

for (d in dates) print(.Date(d))
# [1] "1939-06-10"
# [1] "1932-02-22"
# [1] "1980-03-13"
# [1] "1987-03-17"
# [1] "1988-04-14"
# [1] "1979-08-28"
# [1] "1992-07-16"
# [1] "1989-12-11"

This is equivalent to as.Date(d, origin = '1970-01-01'), the numeric method for as.Date.

Funnily enough, *apply functions don't strip attributes:

invisible(lapply(dates, print))
# [1] "1939-06-10"
# [1] "1932-02-22"
# [1] "1980-03-13"
# [1] "1987-03-17"
# [1] "1988-04-14"
# [1] "1979-08-28"
# [1] "1992-07-16"
# [1] "1989-12-11"

Answer 2

There are multiple way you can handle this :

Loop over index of dates :

for(d in seq_along(dates)){
   print(dates[d])
}

#[1] "1939-06-10"
#[1] "1932-02-22"
#[1] "1980-03-13"
#[1] "1987-03-17"
#[1] "1988-04-14"
#[1] "1979-08-28"
#[1] "1992-07-16"
#[1] "1989-12-11"

Or convert date to list and then print directly.

for(d in as.list(dates)) {
   print(d)
}