removing left hand side parenthesis in str_split in r

Question

How can I make this work in R?

str_split("U.S. (California, San Luis Obispo County)",pattern=' (')

Error in gregexpr("(", "U.S. (California, San Luis Obispo County)", fixed = FALSE, : invalid regular expression '(', reason 'Missing ')''

gregexpr("(", "U.S. (California, San Luis Obispo County)")

Error in gregexpr("(", "U.S. (California, San Luis Obispo County)") : invalid regular expression '(', reason 'Missing ')''

gregexpr("(", "U.S. (California, San Luis Obispo County)",perl=T)

Error in gregexpr("(", "U.S. (California, San Luis Obispo County)", perl = T) : invalid regular expression '('

In addition, warning message:

In gregexpr("(", "U.S. (California, San Luis Obispo County)", perl = T) :
  PCRE pattern compilation error
    'missing )'
    at ''

Is the problem you haven't escaped the parenthesis: `pattern = "\\("`? Parentheses are special in regex. — Hugh, Jun 04 '14 at 05:56
Do you speak about `strsplit` function when you write `str_split` in your first example? — jomuller, Jun 04 '14 at 08:20
Could you add the output expected in your question to undersannd better what you want? — jomuller, Jun 04 '14 at 08:43

jomuller · Answer 1 · 2016-10-07T08:11:23.330

To split using a special character like"(" you have to escape it. To escape a regular expression in R, you have to use a double "\", one for the R character string and another one for the regular expression, as suggested by Hugh. Then your pattern should be "\(". See the regex doc for more information.

The following code does the job

raw_string <- "U.S. (California, San Luis Obispo County)"
splitted_string <- strsplit(x=raw_string, split="\\(")

splitted_string

#[[1]]
#[1] "U.S. "                              
#[2] "California, San Luis Obispo County)"

But I'm not sure that's what you want. If your goal is to remove the left-hand side parenthesis in your character string, use gsub with an empty replacement pattern.

raw_string <- "U.S. (California, San Luis Obispo County)"
no_parenthesis_string <- gsub(pattern="\\(", replacement="", x= raw_string)
no_parenthesis_string 
# [1] "U.S. California, San Luis Obispo County)"

Does it help?

score 0 · Answer 2 · edited Nov 12 '15 at 08:57

0

gsub("\\\\(","",c("U.S. (California, San Luis Obispo County)"))

or

paste0(strsplit(c("U.S. (California, San Luis Obispo County)"), "\\(")[[1]], collapse = "")

Answer: "U.S. California, San Luis Obispo County)"

edited Nov 12 '15 at 08:57

Tunaki

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answered Nov 12 '15 at 08:50

陳奕錩

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removing left hand side parenthesis in str_split in r

2 Answers2