R grep() return whole matching line (similar to the unix grep -A -B?)

Question

I've been searching for a way to ask grep to return a whole line for a matching pattern. Is there functionality for this in R's grep()? I am imagining something like the unix grep arguments -An

Some context: For a paper I've written I want to create a data table or a vector of all citations in a paper. Extracting everything in the paper thats within parentheses using qdapRegex::rm_round() sometimes only returns a year (in the case of citations written like: 'As put forth by Smith (2020)'). It would be nice to grab the whole sentence instead of just '2020'.

Any thoughts? Thank you!

Sure, that's fairly straightforward, depending on your input data. Can you share sample data and your expected result? — Skaqqs, Jan 15 '22 at 00:13

score 2 · Accepted Answer · answered Jan 15 '22 at 03:05

2

grep has an argument value which you can set as TRUE to get the whole string back.

Consider this example where you are looking for numbers.

x <- c('This is 2022', 'This is not a year', '2021 was last year')
grep('\\d+', x)
#[1] 1 3

By default grep returns an index where a match is found.

If you need the complete string as an output -

grep('\\d+', x, value = TRUE)
#[1] "This is 2022"       "2021 was last year"

answered Jan 15 '22 at 03:05

Ronak Shah

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Great, I will try to use this! I was definitely misunderstanding the function of the value argument. I appreciate the clarification on this. – milo Jan 15 '22 at 22:16

score 1 · Answer 2 · answered Jan 15 '22 at 00:16

s <- c("As put forth by Smith (2020)",
       "As put forth by Smith 2020",
       "As put forth by Smith",
       "As put forth (Smith 2020)")

s[grep(pattern = "\\(.*\\)", x = s)]
#> [1] "As put forth by Smith (2020)" "As put forth (Smith 2020)"

Created on 2022-01-14 by the reprex package (v2.0.1)

R grep() return whole matching line (similar to the unix grep -A -B?)

2 Answers2