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str_extract is a function in the R programming language which is used to extract parts of a string that match a certain pattern. It takes two arguments; the string to extract from and the pattern to match. It returns the part of the string that matches the pattern. This is useful for extracting data from strings in a consistent way.
The str_extract() function from the package in R can be used to extract matched patterns in a string.
This function uses the following syntax:
str_extract(string, pattern)
where:
- string: Character vector
- pattern: Pattern to extract
The following examples show how to use this function in practice.
Example 1: Extract One Pattern from String
The following code shows how to extract the string “ther” from a particular string in R:
library(stringr)
#define string
some_string <- "Hey there my name is Doug"
#extract "ther" from string
str_extract(some_string, "ther")
[1] "ther"
The pattern “ther” was successfully extracted from the string.
Note that if we attempt to extract some pattern that doesn’t exist in the string, we’ll simply receive NA as a result:
library(stringr)
#define string
some_string <- "Hey there my name is Doug"
#attempt to extract "apple" from string
str_extract(some_string, "apple")
[1] NA
Since the pattern “apple” did not exist in the string, a value of NA was returned.
Example 2: Extract Numeric Values from String
The following code shows how to use the regex \d+ to extract only the numeric values from a string:
library(stringr)
#define string
some_string <- "There are 350 apples over there"
#extract only numeric values from string
str_extract(some_string, "\d+")
[1] "350"
Example 3: Extract Characters from Vector of Strings
library(stringr)
#define vector of strings
some_strings <- c("4 apples", "3 bananas", "7 oranges")
#extract only characters from each string in vector
str_extract(some_strings, "[a-z]+")
[1] "apples" "bananas" "oranges"
Notice that only the characters from each string are returned.
The following tutorials explain how to perform other common tasks in R: