The substring() function in R can be used to extract a substring in a character vector.

This function uses the following syntax:

substring(text, first, last)

where:

• text: Name of the character vector
• first: The first element to be extracted
• last: The last element to be extracted

Also note that the substr() function does the exact same thing, but with slightly different argument names:

substr(text, first, last)

where:

• x: Name of the character vector
• start: The first element to be extracted
• stop: The last element to be extracted

The examples in this tutorial show how to use the substring() function in practice with the following data frame in R:

#create data frame
df <- data.frame(team=c('Mavericks', 'Hornets', 'Rockets', 'Grizzlies'))

#view data frame
df

       team
1 Mavericks
2   Hornets
3   Rockets
4 Grizzlies

Example 1: Extract Characters Between Certain Positions

The following code shows how to use the substring() function to extract the characters between positions 2 and 5 of the “team” column:

#create new column that contains characters between positions 2 and 5
df$between2_5 <- substring(df$team, first=2, last=5)

#view updated data frame
df

       team  between2_5
1 Mavericks        aver
2   Hornets        orne
3   Rockets        ocke
4 Grizzlies        rizz

Notice that the new column contains the characters between positions 2 and 5 of the “team” column.

Example 2: Extract First N Characters

The following code shows how to use the substring() function to extract the first 3 characters of the “team” column:

#create new column that contains first 3 characters
df$first3 <- substring(df$team, first=1, last=3)

#view updated data frame
df

       team first3
1 Mavericks    Mav
2   Hornets    Hor
3   Rockets    Roc
4 Grizzlies    Gri

Notice that the new column contains the first three characters of the “team” column.

Example 3: Extract Last N Characters

The following code shows how to use the substring() function to extract the last 3 characters of the “team” column:

#create new column that contains last 3 characters
df$last3 <- substring(df$team, nchar(df$team)-3+1, nchar(df$team))

#view updated data frame
df

       team last3
1 Mavericks   cks
2   Hornets   ets
3   Rockets   ets
4 Grizzlies   ies

Notice that the new column contains the last three characters of the “team” column.

Example 4: Replace a Substring

The following code shows how to use the substring() function to replace the first 3 characters of the values in the “team” column with 3 asterisks:

#replace first 3 characters with asterisks in team column
substring(df$team, first=1, last=3) <- "***"

#view updated data frame
df

       team
1 ***ericks
2   ***nets
3   ***kets
4 ***zzlies

Notice that the first three characters of each team name has been replaced with asterisks.

Additional Resources

The following tutorials explain how to perform other common operations with strings in R:

How to Perform Partial String Matching in R