The str_match() function from the package in R can be used to extract matched groups from a string.

This function uses the following syntax:

str_match(string, pattern)

where:

• string: Character vector
• pattern: Pattern to look for

The following examples show how to use this function in practice

Example 1: Use str_match with Vector

The following code shows how to use the str_match() function to extract matched patterns from a character vector:

library(stringr)

#create vector of strings
x <- c('Mavs', 'Cavs', 'Heat', 'Thunder', 'Blazers')

#extract strings that contain 'avs'
str_match(x, pattern='avs')

     [,1] 
[1,] "avs"
[2,] "avs"
[3,] NA   
[4,] NA   
[5,] NA  

The result is a matrix in which each row displays the matched pattern or an NA value if the pattern was not found.

For example:

• The pattern ‘avs’ was found in the first element ‘Mavs’, so ‘avs’ was returned.
• The pattern ‘avs’ was found in the second element ‘Cavs’, so ‘avs’ was returned.
• The pattern ‘avs was not found in the third element ‘Heat’ so NA was returned.

And so on.

Example 2: Use str_match with Data Frame

Suppose we have the following data frame in R:

#create data frame
df <- data.frame(team=c('Mavs', 'Cavs', 'Heat', 'Thunder', 'Blazers'),
                 points=c(99, 104, 110, 103, 115))

#view data frame
df

     team points
1    Mavs     99
2    Cavs    104
3    Heat    110
4 Thunder    103
5 Blazers    115

The following code shows how to use the str_match() function to add a new column to the data frame that either does or does not contain a matched pattern for each team name:

library(stringr)

#create new column
df$match <- str_match(df$team, pattern='avs')

#view updated data frame
df

     team points match
1    Mavs     99   avs
2    Cavs    104   avs
3    Heat    110  <NA>
4 Thunder    103  <NA>
5 Blazers    115  <NA>

The new column titled match contains either the pattern ‘avs’ or NA, depending on whether the pattern is found in the team column.