How to change the values of last two rows in a column for multiple groups?-CodePudding

I have a dataframe with more than 500 rows with columns as below. There are more than 5 groups, 11 rows for each group where each value corresponds to a different month in the year.

    Date        Group
1 2019-07-06     1
2 2019-08-06     1
3 2019-09-06     1
4 2019-09-06     1
5 2019-10-06     1
6 2019-08-06     2
7 2019-09-06     2
8 2019-09-06     2
9 2019-10-06     2

The problem is that there is repetition of 2019-09-06, otherwise it should have been January-November. I want to change the second 2019-09-06 to 2019-10-06 and last row for each group to 2019-11-06.

I thought of using case_when, but it would change both values where month is 09.

Can someone please help me how to do this?

CodePudding user response：

A possible solution:

library(dplyr)

df %>% 
  group_by(Group) %>% 
  mutate(Date = seq(as.Date(first(Date)), length = n(), by="1 month")) %>% 
  ungroup

#> # A tibble: 9 × 2
#>   Date       Group
#>   <date>     <int>
#> 1 2019-07-06     1
#> 2 2019-08-06     1
#> 3 2019-09-06     1
#> 4 2019-10-06     1
#> 5 2019-11-06     1
#> 6 2019-08-06     2
#> 7 2019-09-06     2
#> 8 2019-10-06     2
#> 9 2019-11-06     2