Use regex in R to delete all characters in a string except specified words

Question

Using the R programming language, I want to be able to use the gsub function to remove all characters except two or three specified words.

I've tried a number of methods using look-behind, \\\\bMyWord\\\\b, and the caret symbol ^.

gsub("fbnmobile.*", "" , "fbnmobile akinremi temitope akinfemi gotvnspectran fbn akinremi temitope a and akinsanya arinola o ")

desired output:

"fbnmobile gotvnspectran fbn"

I want a template such that I can add or drop whole words that are to be excepted whenever I delete all of the other characters. In this case, I would specify to delete all characters except for words "fbnmobile", "gotvnspectran", and "fbn".

Also, I'll gladly accept a recommendation for a definitive guide on regular expressions for R.

Answer 1

It may be easier to extract. Specify the pattern of words to extract with OR ( | ) in str_extract_all from stringr and then paste the extracted words to a single string

library(stringr)
paste(str_extract_all(str1, "\\b(fbnmobile|gotvnspectran|fbn)\\b")[[1]], collapse=" ")
#[1] "fbnmobile gotvnspectran fbn"

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Or using gsub

gsub("\\s{2,}", " ", trimws(gsub("\\b(fbnmobile|gotvnspectran|fbn)\\b(*SKIP)(*F)|\\w+", "", str1, perl = TRUE)))
#[1] "fbnmobile gotvnspectran fbn"

daa

str1 <- "fbnmobile akinremi temitope akinfemi gotvnspectran fbn akinremi temitope a and akinsanya arinola o "