Capturing

String Manipulation with stringr in R

Charlotte Wickham

Assistant Professor at Oregon State University

Capturing

ANY_CHAR %R% "a"

<regex> .a

capture(ANY_CHAR) %R% "a"

<regex> (.)a

str_extract(c("Fat", "cat"), 
    pattern = ANY_CHAR %R% "a")

"Fa" "ca"

str_extract(c("Fat", "cat"), 
    pattern = capture(ANY_CHAR) %R% "a")

"Fa" "ca"

str_match()

str_match(c("Fat", "cat"), 
    pattern = capture(ANY_CHAR) %R% "a")

     [,1] [,2]
[1,] "Fa" "F" 
[2,] "ca" "c"

str_match()

pattern <- DOLLAR %R% 
             DGT %R% optional(DGT) %R% 
             DOT %R% 
             dgt(2)

str_view(c("$5.50", "$32.00"), pattern = pattern)

chap_4_1.013.png

str_match()

pattern <- DOLLAR %R% 
             capture(DGT %R% optional(DGT)) %R% 
             DOT %R% 
             capture(dgt(2))

str_match(c("$5.50", "$32.00"), pattern = pattern)

     [,1]     [,2] [,3]
[1,] "$5.50"  "5"  "50"
[2,] "$32.00" "32" "00"

Non-capturing groups

or("dog", "cat")

<regex> (?:dog|cat)

chap_4_1.021.png

Non-capturing groups

or("dog", "cat")

<regex> (?:dog|cat)

chap_4_1.023.png

or("dog", "cat", capture = TRUE)

<regex> (dog|cat)

capture(or("dog", "cat"))

<regex> ((?:dog|cat))

Let's practice!

String Manipulation with stringr in R