How to display real dates in a loop in r - 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", "1980-03-13", "1987-03-17",
"1988-04-14", "1979-08-28", "1992-07-16", "1989-12-11"), tryFormats = c("%Y-%m-%d"))
for(d in dates){
print(d)
}
The output is as follows:
[1] -11163
[1] -13828
[1] 3724
[1] 6284
[1] 6678
[1] 3526
[1] 8232
[1] 7284
How do I get R to print out the actual dates?
So the output reads:
[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"
Thank you!

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)
}