Regular expression to extract all text after "--!!" in R dplyr

Question

I am trying to use dplyr in R to extract substrings after a variable string in a dataframe filtered by certain instances of the variable name in the example below. I am trying to pass the desired result into a new variable called income_rent.

I am new to regular expressions. My attempt to do this is:

income_cashrent <- v18 %>% 
filter(str_detect(name, "B25122")) %>% 
mutate(income_rent = str_extract(label, "[^--!!]*$"))

However, I get the result: Error in stri_extract_first_regex(string, pattern, opts_regex = opts(pattern)) : Syntax error in regexp pattern. (U_REGEX_RULE_SYNTAX)

The first four lines of name are:

Estimate!!Total
Estimate!!Total!!Household income in the past 12 months (in 2018 inflation-adjusted dollars) --!!Less than $10,000
Estimate!!Total!!Household income in the past 12 months (in 2018 inflation-adjusted dollars) --!!Less than $10,000!!With cash rent
Estimate!!Total!!Household income in the past 12 months (in 2018 inflation-adjusted dollars) --!!Less than $10,000!!With cash rent!!Less than $100

The desired result would be:

[not sure how to indicate an empty result here]
Less than $10,000
Less than $10,000!!With cash rent
Less than $10,000!!With cash rent!!Less than $100

I have been thus far unable to debug this, consulting other regex examples on stack. Any guidance would be most welcome. Thanks all in advance!

Answer 1

We can use str_extract to extract the characters after the pattern--!!` using regex lookaround

library(stringr)
library(dplyr)
 v18 %>%        
     mutate(income_rent = str_extract(label, "(?<=--!!).*"))                                                                                                                                                label
#1                                                                                                                                    Estimate!!Total
#2                                 Estimate!!Total!!Household income in the past 12 months (in 2018 inflation-adjusted dollars) --!!Less than $10,000
#3                 Estimate!!Total!!Household income in the past 12 months (in 2018 inflation-adjusted dollars) --!!Less than $10,000!!With cash rent
#4 Estimate!!Total!!Household income in the past 12 months (in 2018 inflation-adjusted dollars) --!!Less than $10,000!!With cash rent!!Less than $100
 #                                       income_rent
#1                                              <NA>
#2                                 Less than $10,000
#3                 Less than $10,000!!With cash rent
#4 Less than $10,000!!With cash rent!!Less than $100

Or another option is str_match

v18$income_rent <-  str_match(v18$label, ".*--!!(.*)")[,2]

data

v18 <- structure(list(label = c("Estimate!!Total", "Estimate!!Total!!Household income in the past 12 months (in 2018 inflation-adjusted dollars) --!!Less than $10,000", 
"Estimate!!Total!!Household income in the past 12 months (in 2018 inflation-adjusted dollars) --!!Less than $10,000!!With cash rent", 
"Estimate!!Total!!Household income in the past 12 months (in 2018 inflation-adjusted dollars) --!!Less than $10,000!!With cash rent!!Less than $100"
)), class = "data.frame", row.names = c(NA, -4L))