padding spaces inside/ in the middle of string to specific number of characters

Question

I have a vector of strings that should each have 8 alphanumeric characters. They might include one or more spaces within the string, not right or left.

For those strings that are less than 8 characters, I'd like to pad the existing spaces, so that in the end all strings have 8 characters. The spaces / padding shall remain within the string. (Background: this is related to UK post codes)

My approach is convoluted and possibly flawed, below an example vector and desired output.

## x can take any alphanumeric value
x <- c("xxx xxx", "xx xxx", "x  xxx", "xxx  xxx", "xx   xxx", "xxxxxxxx")

## missing number of spaces
s_miss <- 8 - nchar(x)
## numbers of spaces
s_pres <- stringr::str_count(x, "\\s")

## now here is a convoluted function
## if a space is found, the missing spaces will be added to the already present spaces
padded <- sapply(1: length(x), function(i){
    gsub("\\s+", paste(rep(" ", s_pres[i] + s_miss[i]), collapse = ""), x[i])})

## desired output 
padded
#> [1] "xxx  xxx" "xx   xxx" "x    xxx" "xxx  xxx" "xx   xxx" "xxxxxxxx"
nchar(padded)
#> [1] 8 8 8 8 8 8

Answer 1

regmatches(x, regexpr(' ', x)) <- strrep(' ', 9 - nchar(x))
x
[1] "xxx  xxx" "xx   xxx" "x    xxx" "xxx  xxx" "xx   xxx" "xxxxxxxx"

Or even:

 stringr::str_replace(x, ' ', strrep(' ', 9 - nchar(x)))