Insert specific character in front of specific pattern in R

Question

I want to insert a specific character ("+") in front of the character "b" as part of a string in R. So for example "2b^3" should be converted to "2+b^3" or "200b" to "200+b". How can I achieve this?

Edit: I have a follow up question to the one before:

I have tried this answer: Extract a substring according to a pattern

But it doesn't work for ^:

string = "2+b^3"
sub(".*^", "", string)

gives me still "2+b^3" and I would like to receive "3".

What can I do?

score 1 · Accepted Answer · answered Jun 05 '22 at 19:47

1

A possible solution, in base R:

gsub("b", "+b", "2b^3")

#> [1] "2+b^3"

Or using stringr::replace:

stringr::str_replace("2b^3", "b", "+b")

#> [1] "2+b^3"

answered Jun 05 '22 at 19:47

PaulS

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thank you very much, do you have an answer to the follow up question as well? would really appreciate it! – dlwhch Jun 05 '22 at 20:47
@Thefourthbird has already offered you a solution! – PaulS Jun 06 '22 at 11:51

score 1 · Answer 2 · answered Jun 06 '22 at 08:30

If the b char is always prepended by a digit, you can capture the digits and use the capture group in the replacement.

gsub("(\\d)b", "\\1+b", "2b^3")

Output (R demo)

[1] "2+b^3"

For the second part you have to escape the caret \^ or else it would denote the start of the string.

string = "2+b^3"
sub(".*\\^", "", string)

Output (R demo)

Insert specific character in front of specific pattern in R

2 Answers2