Group by ID and keep latest date

March 22, 2022

I have a dataset that looks like this

 ID       date
 1        2020-05-01
 1        2020-06-13
 2        2021-01-02
 2        2021-01-02
 3        2022-01-07
 3        2021-12-14

And so on. There are about 30 variables in my dataset. I want to group by ID, and rewrite df$date such that only the latest date remains for each ID:

ID       date
 1        2020-06-13
 1        2020-06-13
 2        2021-01-02
 2        2021-01-02
 3        2022-01-07
 3        2022-01-07

Date is formatted as "%Y-%m-%d"

>Solution :

You can use an if_else statement to check for latest date, and replace any date that is not the latest.

library(dplyr)

df %>% 
  group_by(ID) %>% 
  mutate(date = if_else(date == max(date), as.Date(date), as.Date(max(date))))

# A tibble: 6 × 2
# Groups:   ID [3]
     ID date      
  <int> <date>    
1     1 2020-06-13
2     1 2020-06-13
3     2 2021-01-02
4     2 2021-01-02
5     3 2022-01-07
6     3 2022-01-07