regex - Regular expression to add 0s to beginning of string -

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• adding leading zeros using r 7 answers

i'm new regular expressions , i'm have trouble putting them @ moment. i'm working r @ moment, , i'm looking ensure strings in character vector of length 3.

so have character vector of following:

['1','23','113'] 

what regular expression able use ensure length of each string 3 , in cases less, add 0's start?

so output looking be:

['001','023','113'] 

an explanation alongside answer appreciated, thanks.

edit: length of strings in character vector greater or equal 1 , less or equal 3.

instead of regex, @ sprintf function:

x <- c(1, 23, 113) x # [1]   1  23 113 sprintf("%03d", x) # [1] "001" "023" "113" 

as dealing character vector, need use as.numeric first:

x <- as.character(x) sprintf("%03d", x) ## won't work # error in sprintf("%03d", x) :  #   invalid format '%03d'; use format %s character objects sprintf("%03d", as.numeric(x)) # [1] "001" "023" "113"