r - pad numeric column with leading zeros -

i've been looking past few hours. have tried using sprintf changes column character. want have fixed-width numeric column, padded zeros.

if you're willing use custom class, can write print method this. make data frame, , give custom class:

df <- data.frame(a=letters[1:10], b=sample(c(1, 10, 100), 10, rep=t), c=sample(c(1, 10, 100), 10, rep=t)) class(df) <- c("my_df", class(df)) 

write print method uses @benbolker's formatting:

print.my_df <- function(x, ...) {   num.cols <- sapply(x, is.numeric)   x[num.cols] <- lapply(x[num.cols], sprintf, fmt="%04d")   nextmethod() } 

and then:

df 

produces:

      b    c 1  0100 0100 2  b 0010 0001 3  c 0001 0010 4  d 0001 0100 5  e 0001 0001 6  f 0001 0001 7  g 0001 0001 8  h 0001 0100 9  0001 0100 10 j 0001 0001 

you can still use data frame same way since numbers converted when printed.

> sum(df$b) [1] 118