r - Create end of the month date from a date variable

Question

I have a large data frame with date variables, which reflect first day of the month. Is there an easy way to create a new data frame date variable that represents the last day of the month?

Below is some sample data:

date.start.month=seq(as.Date("2012-01-01"),length=4,by="months")
df=data.frame(date.start.month)
df$date.start.month

"2012-01-01" "2012-02-01" "2012-03-01" "2012-04-01"

I would like to return a new variable with:

"2012-01-31" "2012-02-29" "2012-03-31" "2012-04-30"

I've tried the following but it was unsuccessful:

df$date.end.month=seq(df$date.start.month,length=1,by="+1 months")

Answer 1

To get the end of months you could just create a Date vector containing the 1st of all the subsequent months and subtract 1 day.

date.end.month <- seq(as.Date("2012-02-01"),length=4,by="months")-1
date.end.month
[1] "2012-01-31" "2012-02-29" "2012-03-31" "2012-04-30"