R Increment Dates by Periods across data frame columns

Question

I'm trying to do some tests around measurement periods in time. I'd like to increment the size of the measurement bins (ie 1 month vs 2 months, etc.).

I have a data frame with a date seq() which works fine my problem is with incrementing the date by a month, week, etc.

df1 <- data.frame(id = 1:20, date1 = seq(as.Date('2012-01-01'),by = 'month', len = 20))
df1$date2 <- df1$date1 + 30

This is obviously wrong if I want the 1st of each month or week. Is there a function or package for this type of issue?

EDIT:

This :

seq( x, by = "month", length.out = 1)

seems to work for individual cells, but won't work for a column as it returns a numeric:

df1$date2 <- sapply(df1$date1, function(x) seq( x, by = "month", length.out = 1))

> head(df1)
  id      date1 date2
1  1 2012-01-01 15340
2  2 2012-02-01 15371
3  3 2012-03-01 15400
4  4 2012-04-01 15431
5  5 2012-05-01 15461
6  6 2012-06-01 15492

Answer 1

It sounds like you're looking for cut:

df1$date2 <- cut(df1$date1 + as.difftime(31, units='days'), breaks='months')
df1$date3 <- cut(df1$date2 + as.difftime(1, units='weeks'), breaks='weeks')

Answer 2

There might be more elegant solutions but this should work -

df1$date2 <- as.Date(
   paste(
      ifelse(
         strftime(df1$date1,'%m') == 12,  
         as.integer(strftime(df1$date1,'%Y')) + 1,
         as.integer(strftime(df1$date1,'%Y'))
      ),
      ifelse(
         strftime(df1$date1,'%m') == 12,  
         1,
         as.integer(strftime(df1$date1,'%m')) + 1
      ),
      1,
      sep = "-"
   ),
"%Y-%m-%d"
)