Regular expression in R, splitting sentence at keywords in R - r

Question

Hi,
I would like to split the sentence into two portions, from everything keyword_1 to keyword_2, and keyword_2 to the end of the sentence, preferably using regular expressions.
For example (my ideal output - shown below):
Below is a data set that I made.
Data set
library(tibble)
keyword_1 <- c("coffee", "apple", "rainbow", "strawberry shortcake")
keyword_2 <- c("life", "new york", "seven colours", "sweet and yummy")
raw <-
tibble(
sentence = c(
"coffee is keyword_1_1 life is keyword_2_1",
"apple is keyword_1_2 new york is keyword_2_2",
"rainbow is keyword_1_3 seven colours is keyword_2_3",
"strawberry shortcake is keyword_1_4 sweet and yummy is keyword 2_4"
))
raw
#> # A tibble: 4 x 1
#> sentence
#> <chr>
#> 1 coffee is keyword_1_1 life is keyword_2_1
#> 2 apple is keyword_1_2 new york is keyword_2_2
#> 3 rainbow is keyword_1_3 seven colours is keyword_2_3
#> 4 strawberry shortcake is keyword_1_4 sweet and yummy is keyword 2_4
Intended Output
library(tibble)
output = tibble(
output1 = c(
"coffee is keyword_1_1",
"apple is keyword_1_2",
"rainbow is keyword_1_3",
"strawberry shortcake is keyword_1_4"
),
output2 = c("life is keyword_2_1", "new york is keyword_2_2",
"seven colours is keyword_2_3", "sweet and yummy is keyword 2_4")
)
output
#> # A tibble: 4 x 2
#> output1 output2
#> <chr> <chr>
#> 1 coffee is keyword_1_1 life is keyword_2_1
#> 2 apple is keyword_1_2 new york is keyword_2_2
#> 3 rainbow is keyword_1_3 seven colours is keyword_2_3
#> 4 strawberry shortcake is keyword_1_4 sweet and yummy is keyword 2_4
Created on 2021-03-18 by the reprex package (v0.3.0)
devtools::session_info()
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#> tz Australia/Melbourne
#> date 2021-03-18
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Answer 1

Assuming that the pattern is always "keyword_number_number", so that the fourth entrance is missing a "_" and should be:
raw[4,1] = "strawberry shortcake is keyword_1_4 sweet and yummy is keyword_2_4"
Then we can write:
pattern = "([a-z ]+ keyword_[0-9]_[0-9]) ([a-z ]+ keyword_[0-9]_[0-9])"
a = matrix(NA, nrow(raw), 2)
for(i in 1:nrow(raw)){
for(j in 1:2)
a[i,j] = gsub(pattern, paste0("\\",j), raw[i,1])}
Output:
> a
[,1] [,2]
[1,] "coffee is keyword_1_1" "life is keyword_2_1"
[2,] "apple is keyword_1_2" "new york is keyword_2_2"
[3,] "rainbow is keyword_1_3" "seven colours is keyword_2_3"
[4,] "strawberry shortcake is keyword_1_4" "sweet and yummy is keyword_2_4"

Answer 2

here is a data.table approach, using a look-behind regex pattern for splitting
library( data.table )
setDT(raw)[, paste0( "output", 1:2 ) :=
lapply( tstrsplit(sentence, "(?<=_[0-9]{1}_[0-9]{1})", perl = TRUE ),
trimws ) ][, sentence := NULL][]
# output1 output2
# 1: coffee is keyword_1_1 life is keyword_2_1
# 2: apple is keyword_1_2 new york is keyword_2_2
# 3: rainbow is keyword_1_3 seven colours is keyword_2_3
# 4: strawberry shortcake is keyword_1_4 sweet and yummy is keyword 2_4