How to replace NA with most recent non-NA by group? [duplicate]

Answer 1

Could also be:

library(dplyr)
library(tidyr)
df %>% group_by(name) %>% fill(age, birthplace)

# Source: local data frame [8 x 4]
# Groups: name [4]

#     name   age birthplace value
#   <fctr> <dbl>     <fctr> <int>
# 1      A    28      city1   100
# 2      A    28      city1   101
# 3      B    NA      city2   102
# 4      B    NA      city2   103
# 5      B    NA      city2   104
# 6      C    NA         NA   105
# 7      D    53         NA   106
# 8      D    53         NA   107

Answer 2

This is a base R solution:

do.call(rbind,lapply(split(df, df$name), function(x) {
    tempdf <- x
    if (nrow(tempdf) > length(which(is.na(x$birthplace)))) {
        tempdf[which(is.na(x$birthplace)),c("age","birthplace")] <- tempdf[which(is.na(x$birthplace))[1]-1,c("age","birthplace")]
    }
    return(tempdf)
}))

Output:

 name age birthplace value
 A    28  city1      100  
 A    28  city1      101  
 B    NA  city2      102  
 B    NA  city2      103  
 B    NA  <NA>       104  
 C    NA  <NA>       105  
 D    53  <NA>       106  
 D    NA  <NA>       107