I'm trying to create a filter for large dataframe. I'm trying to use grepl to search for a series of text within a specific column. I've done this for single words/combinations, but now I want to search for two words in close proximity (ie the word tumo(u)r within 3 words of the word colon).

I've checked my regular expression on https://www.regextester.com/109207 and my search works there, but it doesn't work within R.

The error I get is Error: '\W' is an unrecognized escape in character string starting ""\btumor|tumour)\W"

Example below - trying to search for tumo(u)r within 3 words of cancer.

Can anyone help?

library(tibble)
example.df <- tibble(number = 1:4, AB = c('tumor of the colon is a very hard disease to cure', 'breast cancer is also known as a neoplasia of the breast', 'tumour of the colon is bad', 'colon cancer is also bad'))

filtered.df <- example.df %>% 
    filter(grepl(("\btumor|tumour)\W|\w (\w \W ){0,3}colon\b"), AB, ignore.case=T) 

CodePudding user response：

R uses backslashes as escapes and the regex engine does,too. Need to double your backslashes. This is explained in multiple prior questions on StackOverflow as well as in the help page brought up at ?regex. You should try to use the escaped operators in a more simple set of tests before attempting complex operations. And you should pay better attention to the proper placement of parentheses and quotes in the pattern argument.

filtered.df <- example.df %>% 

   #filter(grepl(("\btumor|tumour)\W|\w (\w \W ){0,3}colon\b"), AB, 

# errors here ....^.^..............^..^...^..^.............^.^

    filter(grepl( "(\\btumor|tumour)\\W|\\w (\\w \\W ){0,3}colon\\b", AB,
ignore.case=T) )

> filtered.df
# A tibble: 2 × 2
  number AB                                               
   <int> <chr>                                            
1      1 tumor of the colon is a very hard disease to cure
2      3 tumour of the colon is bad