fill column with previous column if NA

Question

I have a data frame like this

df <- data.frame(v1 = 10:14, v2 = c(NA, 1, NA, 3, 6), v3 = c(1, NA, NA, 9, 4))

  v1 v2 v3
1 10 NA  1
2 11  1 NA
3 12 NA NA
4 13  3  9
5 14  6  4

I now want to fill the NAs with the value of the previous column, so it looks like this:

  v1 v2 v3
1 10 10  1
2 11  1  1
3 12 12 12
4 13  3  9
5 14  6  4

I know how to do this manually, like this:

df$v2 <- ifelse(is.na(df$v2), df$v1, df$v2)

How can I automate this for a full data frame with many columns?

Answer 1

You can do this with fill from tidyr:

library(dplyr)
library(tidyr)

data.frame(t(df)) %>%
  fill(., names(.)) %>%
  t()

Result:

   v1 v2 v3
X1 10 10  1
X2 11  1  1
X3 12 12 12
X4 13  3  9
X5 14  6  4

Note:

Basically, I transposed df, filled every column downward, then transposed it back to the original orientation