如何基于R中的条件将单元格的值传播到其他行

Question

I have a data frame that looks like the following:

index    A    B    correct
1        1    1    -
2        1    2    -
3        1    3    0
4        2    1    -
5        2    2    -
6        2    3    1

I would like to propagate the value of 'correct' to other rows when A matches. Ie the desired output:

index    A    B    correct
1        1    1    0
2        1    2    0
3        1    3    0
4        2    1    1
5        2    2    1
6        2    3    1

So all the rows that has A = 1 will have the same value of correct, which is propagated from row(A=1,B=3).

How should I do this in R? I have a big dataframe with many columns and it is seems that using loops to manipulate dataframes is not recommended in R. Any help would be greatly appreciated!

Answer 1

 transform(A,correct=zoo::na.locf0(correct,T))
  index A B correct
1     1 1 1       0
2     2 1 2       0
3     3 1 3       0
4     4 2 1       1
5     5 2 2       1
6     6 2 3       1