repeat existed row for a column based on another column

I have a dataframe like following:

df<- data.frame(ID=c(1,1,1,2,2,3,3,3,4,4),weight=c(0,0,11,0,10,12,0,0,13,0))

I want to repeat the value of column weight based on column ID.
my expected output would be like this:

   ID      weight
1   1     11
2   1     11
3   1     11
4   2     10
5   2     10
6   3     12
7   3     12
8   3     12
9   4     13
10  4     13

by the code below I have got some error:

df1<- df %>% group_by(ID) %>% rep(weight)

>Solution :

You may try

library(dplyr)
df %>%
  group_by(ID) %>%
  mutate(weight = sum(unique(weight)))

      ID weight
   <dbl>  <dbl>
 1     1     11
 2     1     11
 3     1     11
 4     2     10
 5     2     10
 6     3     12
 7     3     12
 8     3     12
 9     4     13
10     4     13