split on last occurrence of digit, take 2nd part

Question

If I have a string and want to split on the last digit and keep the last part of the split hpw can I do that?

x <- c("ID", paste0("X", 1:10, state.name[1:10]))

I'd like

 [1] NA            "Alabama"     "Alaska"      "Arizona"     "Arkansas"   
 [6] "California"  "Colorado"    "Connecticut" "Delaware"    "Florida"    
[11] "Georgia"    

But would settle for:

 [1] "ID"          "Alabama"     "Alaska"      "Arizona"     "Arkansas"   
 [6] "California"  "Colorado"    "Connecticut" "Delaware"    "Florida"    
[11] "Georgia"    

I can get the first part by:

unlist(strsplit(x, "[^0-9]*$"))

But want the second part.

Thank you in advance.

Answer 1

You can do this one easy step with a regular expression:

gsub("(^.*\\d+)(\\w*)", "\\2", x)

Results in:

 [1] "ID"          "Alabama"     "Alaska"      "Arizona"     "Arkansas"    "California"  "Colorado"    "Connecticut"
 [9] "Delaware"    "Florida"     "Georgia"  

---

What the regex does:

1. "(^.*\\d+)(\\w*)": Look for two groups of characters.
   • The first group (^.*\\d+) looks for any digit followed by at least one number at the start of the string.
   • The second group \\w* looks for an alpha-numeric character.
2. The "\\2" as the second argument to gsub() means to replace the original string with the second group that the regex found.