adding 1 month to a date

Question

I want to get the date sequence between a startDate and endDate by adding 1 month to the startDate. ie, if startDate is 2013-01-31 and endDate is 2013-07-31, I would prefer to see dates like this:

"2013-01-31" "2013-02-28" "2013-03-31" "2013-04-30" "2013-05-31" "2013-06-30" "2013-07-31"

I have tried

seq.Date(as.Date("2013-01-31"),by="month",length.out=7)

But the output of this code is like this

> seq.Date(as.Date("2013-01-31"),by="month",length.out=7)
[1] "2013-01-31" "2013-03-03" "2013-03-31" "2013-05-01" "2013-05-31" "2013-07-01" "2013-07-31"

So, what is the simplest solution to get the correct output?

Solution 1

I have to work with dates in R, and one of the most useful packages that I found for date data is lubridate. For your problem, you can simply do the following:

require(lubridate)
# ymd function parses dates in year-month-day format
startDate <- ymd('2013-01-31')
# The %m+% adds months to dates without exceeding the last day
myDates <- startDate %m+% months(c(0:6))

lubridate also has many other functions for dates, and I highly recommend taking a look.

Solution 2

This is not working, because R is not sure what to do with last day of the month. So I have a simple solution: do the same but use 1st day of the next month and then substract 1:

seq(as.Date("2013-02-1"),by="month",length.out=7) - 1
[1] "2013-01-31" "2013-02-28" "2013-03-31" "2013-04-30" "2013-05-31" "2013-06-30" "2013-07-31"