How to modify string in R taking into account the number of symbols you want to modify

Question

This question is very easy to understand, but I can't wrap my head around how to get a solution. Let's say I have a vector and I want to modify it so it would have 5 integers at the end, and missing digits are replaced with zeros:

Smth1     Smth00001
Smth22    Smth00022
Smth333   Smth00333
Smth4444  Smth04444
Smth55555 Smth55555

I guess it can be done with regex and functions like gsub, but don't understand how to take into account the length of the replaced string

not really, dww. One person proposed str_pad from stringr and it really solves the issue, though the person asked about smth else — Poiu Rewq, Jul 14 '16 at 19:59

score 2 · Answer 1 · answered Jul 14 '16 at 16:16

Here's an idea using stringi:

v <- c("Smth1", "Smth22", "Smth333", "Smth4444", "Smth55555")

library(stringi)
d <- stri_extract(v, regex = "[:digit:]+")
a <- stri_extract(v, regex = "[:alpha:]+")
paste0(a, stri_pad_left(d, 5, "0"))

Which gives:

[1] "Smth00022" "Smth00333" "Smth04444" "Smth55555"

score 2 · Answer 2 · answered Jul 14 '16 at 16:56

2

Using base R. Someone else can prettify the regex:

sprintf("%s%05d", gsub("^([^0-9]+)..*$", "\\1", x),
  as.numeric(gsub("^..*[^0-9]([0-9]+)$", "\\1", x)))

[1] "Smth00001" "Smth00022" "Smth00333" "Smth04444" "Smth55555"

answered Jul 14 '16 at 16:56

Zelazny7

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score 2 · Answer 3 · edited May 23 '17 at 11:58

Here is a simple 1-line solution similar to Zelazny's but using a replace callback method inside a gsubfn using gsubfn library:

> library(gsubfn)
> v <- c("Smth1", "Smth22", "Smth333", "Smth4444", "Smth55555")
> gsubfn('[0-9]+$', ~ sprintf("%05d",as.numeric(x)), v)
[1] "Smth00001" "Smth00022" "Smth00333" "Smth04444" "Smth55555"

The regex [0-9]+$ (see the regex demo) matches 1 or more digits at the end of the string only due to the $ anchor. The matched digits are passed to the callback (~) and sprintf("%05d",as.numeric(x)) pads the number (parsed as a numeric with as.numeric) with zeros.

To only modify strings that have 1+ non-digit symbols at the start and then 1 or more digits up to the end, just use this PCRE-based gsubfn:

> gsubfn('^[^0-9]+\\K([0-9]+)$', ~ sprintf("%05d",as.numeric(x)), v, perl=TRUE)
[1] "Smth00001" "Smth00022" "Smth00333" "Smth04444" "Smth55555"

where

^ - start of string
[^0-9]+\\K - matches 1+ non-digit symbols and \K will omit them
([0-9]+) - Group 1 passed to the callback
$ - end of string.

FYI, this solution is the only one among those present that uses 1 regex match operation. — Wiktor Stribiżew, Jul 14 '16 at 17:56
I don't know why we are all getting downvoted. Very elegant solution BTW +1 — Steven Beaupré, Jul 14 '16 at 19:17

score -1 · Answer 4 · answered Jul 14 '16 at 16:23

Here a solution using the library stringr:

library(stringr)
library(dplyr)

num <- str_extract(v, "[1-9]+")
padding <- 9 - nchar(num)
ouput <- paste0(str_extract(v, "[^0-9]+") %>% 
                str_pad(width = padding, side = c("right"), pad = "0"), num)

The output is:

"Smth00001" "Smth00022" "Smth00333" "Smth04444" "Smth55555"

score -1 · Answer 5 · answered Jul 14 '16 at 17:51

-1

library(stringr)
paste0(str_extract(v,'\\D+'),str_pad(str_extract(v,'\\d+'),5,'left', '0'))
#[1] "Smth00001" "Smth00022" "Smth00333" "Smth04444" "Smth55555"

answered Jul 14 '16 at 17:51

Shenglin Chen

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How is this any different from my solution with `stringi` ? – Steven Beaupré Jul 14 '16 at 19:18

How to modify string in R taking into account the number of symbols you want to modify

5 Answers5