Add leading 0 with gsub

Question

I would like to add leading zeros to an alphanumeric string for a total of ten characters. It is possible, however, that there is a space in between the characters.

TestID <- c("1b4 7A1")

gsub(" ","0",sprintf("%010s", TestID))

This code adds leading zeros, but also replaces the empty space within the string with a zero. Is there a way to add the zeros only in front of the string?

# [1] "0001b4 7A1"

Answer 1

You could use str_pad from package stringr and do:

str_pad(TestID, width=10, side="left", pad="0")

This gives:

> str_pad(TestID, width=10, side="left", pad="0")
[1] "0001b4 7A1"

Answer 2

We can use sub

sub('^', paste(rep(0,3), collapse=''), TestID)
#[1] "0001b4 7A1"

If it is to add 0 at the front

paste0('000', TestID)

Answer 3

A base R solution for strings of variable lengths could be

paste0(paste(rep("0", 10 - nchar(TestID)), collapse=''), TestID)
# [1] "0001b4 7A1"

Answer 4

Can also use the stringi package.

library(stringi)
stri_pad_left(TestID, pad="0", width=10)
# [1] "0001b4 7A1"