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 Use str_replace in R
How to Perform Partial String Matching in R
How to Convert Strings to Dates in R
How to Convert Character to Numeric in R
