Create new column based on count of occurrences based on conditions

I want to create a new column based on the count of scores that are >= 3 according to the date.

For example, for dates that have multiple occurrences such as 2020-12-07, there is only 1 score that is >= 3, so the value for the new column num_greater_than_3 is 1 for both of the 2020-12-07 dates.

original:

ID <- c(1,1,1,1,1,1,1,1,1)
date <- c("2020-12-02","2020-12-03","2020-12-04","2020-12-05","2020-12-06","2020-12-07","2020-12-07,"2020-12-08","2020-12-08)
score <- c(2,5,2,2,3,3,1,1,3)
a <- data.frame(ID,date,score)

desired:

ID <- c(1,1,1,1,1,1,1,1,1)
date <- c("2020-12-02","2020-12-03","2020-12-04","2020-12-05","2020-12-06","2020-12-07","2020-12-07,"2020-12-08","2020-12-08)
score <- c(2,5,2,2,3,3,1,1,3)
num_score_greater_than_3 <- (0,1,0,0,1,1,1,1,1)
a <- data.frame(ID,date,score,num_score_greater_than_3)

I appreciate all the help there is! Thanks!

>Solution :

I assume you want greater than or equal to 3:

library(dplyr)

a %>% 
  group_by(date) %>%
  mutate(num_score_greater_than_3=sum(score>=3))

     ID date       score num_score_greater_than_3
  <dbl> <fct>      <dbl>                    <int>
1     1 2020-12-02     2                        0
2     1 2020-12-03     5                        1
3     1 2020-12-04     2                        0
4     1 2020-12-05     2                        0
5     1 2020-12-06     3                        1
6     1 2020-12-07     3                        1
7     1 2020-12-07     1                        1
8     1 2020-12-08     1                        1
9     1 2020-12-08     3                        1