Using lubridate function to conditionally change year in date

Question

So I am currently struggling to change the year part of a date using an if function.

My date column looks like this (there are many more values in the real dataframe so it can not be a manual solution):

Date
<S3: POSIXct>
2020-10-31
2020-12-31

I essentially want to create an if command (or any other method) such that if the month is less than 12 (ie. not December) then the year is increased by 1.

So far I have tried using the lubridate package to do:

if (month(df$Date)<12) {
df$Date <- df$Date %m+% years(1)
}

However the function seems to not be conditioning correctly and is instead adding one to every year including those where the month=12

Any help would be greatly appreciated!

Answer 1

You could approach it like this:

library(lubridate)

dates <- seq.Date(from = as.Date('2015-01-01'),
                  to = Sys.Date(),
                  by = 'months')
indicator <- month(dates) < 12

dates2 <- dates
dates2[indicator] <- dates[indicator] %m+% years(1)

res <- data.frame(dates, indicator, dates2)
> head(res, 25)
        dates indicator     dates2
1  2015-01-01      TRUE 2016-01-01
2  2015-02-01      TRUE 2016-02-01
3  2015-03-01      TRUE 2016-03-01
4  2015-04-01      TRUE 2016-04-01
5  2015-05-01      TRUE 2016-05-01
6  2015-06-01      TRUE 2016-06-01
7  2015-07-01      TRUE 2016-07-01
8  2015-08-01      TRUE 2016-08-01
9  2015-09-01      TRUE 2016-09-01
10 2015-10-01      TRUE 2016-10-01
11 2015-11-01      TRUE 2016-11-01
12 2015-12-01     FALSE 2015-12-01
13 2016-01-01      TRUE 2017-01-01
14 2016-02-01      TRUE 2017-02-01
15 2016-03-01      TRUE 2017-03-01
16 2016-04-01      TRUE 2017-04-01
17 2016-05-01      TRUE 2017-05-01
18 2016-06-01      TRUE 2017-06-01
19 2016-07-01      TRUE 2017-07-01
20 2016-08-01      TRUE 2017-08-01
21 2016-09-01      TRUE 2017-09-01
22 2016-10-01      TRUE 2017-10-01
23 2016-11-01      TRUE 2017-11-01
24 2016-12-01     FALSE 2016-12-01
25 2017-01-01      TRUE 2018-01-01