Add a number prefix to a regular expression in r

[moh.ali.square]

Hi,

I have a list contains characters with different lengths, I want to add prefix for characters with specific length.

library(tidyverse)

a = list("20013536", "20017954","19618","18114")
a

[[1]]
[1] "20013536"

[[2]]
[1] "20017954"

[[3]]
[1] "19618"

[[4]]
[1] "18114"

I want to add the numerical prefix "200" to the third and fourth elements of the list.

Thank you in advance.

Regards,
Mohamed.

[cderv]

@moh.ali.square

a = list("20013536", "20017954","19618","18114")

Is this conditional to the length of the string ? Like if only 5 digits, add 200 before ?

a = c("20013536", "20017954","19618","18114")


# iterate
purrr::map_chr(a, ~{
  if (nchar(.x) == 5) paste0("200", .x) else .x
})
#> [1] "20013536" "20017954" "20019618" "20018114"

# vectorise
dplyr::if_else(nchar(a) == 5, paste0(200, a), a)
#> [1] "20013536" "20017954" "20019618" "20018114"

^{Created on 2020-08-20 by the reprex package (v0.3.0.9001)}

If you can create a function pad_if_only_five() to apply each time you need.

[moh.ali.square]

Thanks cderv,

the code worked well as a is a vector, when I tried to apply the code on a list, it through an erro

Error: unexpected '}' in:
" + if (nchar(.x) == 5) paste0("200", .x) else .x
+ }"

I am trying to use the code with list, even with lapply, but I'm not able to fix it.

Thank you in advance for your support.

Regards,
Mohamed.

[cderv]

It works with list also,

a = list("20013536", "20017954","19618","18114")


# iterate
purrr::map_chr(a, ~{
  if (nchar(.x) == 5) paste0("200", .x) else .x
})
#> [1] "20013536" "20017954" "20019618" "20018114"

^{Created on 2020-08-21 by the reprex package (v0.3.0)}

@moh.ali.square

Error: unexpected '}' in:

You seem to have a syntax error in your code