Filling missing value in group

Question

I have data frame where some of the values are missing

A 1
A NA
A NA
B NA
B 2
B NA
C NA
C NA
C NA

How can I fill in groups where I have dat

Answer 1

Alternative solution, though perhaps a bit flawed in how many assumptions it makes:

library(dplyr)
y %>%
  group_by(V1) %>%
  arrange(V2) %>%
  mutate(V2 = V2[1])
# Source: local data frame [9 x 2]
# Groups: V1 [3]
#      V1    V2
#   (chr) (int)
# 1     A     1
# 2     A     1
# 3     A     1
# 4     B     2
# 5     B     2
# 6     B     2
# 7     C    NA
# 8     C    NA
# 9     C    NA