Looping in R to only add leading zeros to specified length

Question

how would I be able to go from a column like this: 1 1 1 2 3 4 9 25 100

to one like this: 01 01 01 02 03 04 09 25 100

Basically, I want to add a leading zero to any value with only length 1. The actual data frame is much bigger than this. Thanks!

Answer 1

You can use sprintf in base R

vec <-  c(1, 1, 1, 2, 3, 4, 9, 25, 100)

sprintf("%02d", vec)
#> [1] "01"  "01"  "01"  "02"  "03"  "04"  "09"  "25"  "100"

Answer 2

As an alternative str_pad from stringr package:

library(stringr)
str_pad(vec, 2, pad = "0")

[1] "01"  "01"  "01"  "02"  "03"  "04"  "09"  "25"  "100"

Answer 3

You may also want to explore the formatC function:

vec <-  c(1, 1, 1, 2, 3, 4, 9, 25, 100)
formatC(x = vec, digits = 1, flag = "0", format = "d")

Results

"01"  "01"  "01"  "02"  "03"  "04"  "09"  "25"  "100"