Search notes:

R function: strftime

strftime converts a date-time object into a character vector. strptime does the opposite. 
y2000 <- as.Date("2000-01-01")

class(y2000)
# [1] "Date"

y2000_100days <- y2000 + 100

txt <- strftime(y2000_100days, '%F') # ISO 8601

class(txt)
# [1] "character"

txt
# 2000-04-10
Github repository about-r, path: /functions/strftime.R

See also

strftime
Index to (some) R functions

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