How To Use sub() and gsub() in R

Introduction

The sub() and gsub() functions in R will substitute the string or the characters in a vector or a data frame with a specific string. These functions are useful when performing changes on large data sets.

In this article, you will explore how to use sub() and gsub() functions in R.

Prerequisites

To complete this tutorial, you will need:

• R installed locally or on a server.

Syntax of sub() and gsub()

The basic syntax for sub() is:

sub(pattern, replacement, x)

The basic syntax for gsub() is:

gsub(pattern, replacement, x)

The syntax for sub() and gsub() requires a pattern, a replacement, and the vector or data frame:

• pattern: The pattern or the string which you want to be substituted.
• replacement: A input string to substitute the pattern string.
• x: A vector or a data frame to substitute the strings.

The pattern can also be in the form of a regular expression (regex).

Now that you are familiar with the syntax, you can move on to implementation.

The sub() Function in R

The sub() function in R replaces the string in a vector or a data frame with the input or the specified string.

However, the limitation of the sub() function is that it only substitutes the first occurrence.

1. Using the sub() Function

In this example, learn how to substitute a string pattern with a replacement string with the sub() function.

# the input vector 
df<-"R is an open-source programming language widely used for data analysis and statistical computing."

# the replacement
sub('R','The R language',df)

Running this command generates the following output:

Output
"The R language is an open-source programming language widely used for data analysis and statistical computing."

The sub() function replaces the string 'R' in the vector with the string 'The R language'.

In this example, there was a single occurrence of pattern matching. Consider what happens if there are multiple occurrences of pattern matches.

# the input vector
df<-"In this tutorial, we will install R and show how to add packages from the official Comprehensive R Archive Network (CRAN)."

# the replacement
sub('R','The R language',df)

Running this command generates the following output:

"In this tutorial, we will install The R language and show how to add packages from the official Comprehensive R Archive Network (CRAN)."

In this example, you can observe that the sub() function replaced the first occurrence of the string 'R' with 'The R language'. But the next occurrence in the string remains the same.

2. Using the sub() Function with a Data Frame

The sub() function also works with data frames.

# creating a data frame
df<-data.frame(Creature=c('Starfish','Blue Crab','Bluefin Tuna','Blue Shark','Blue Whale'),Population=c(5,6,4,2,2))

# data frame
df

This will create the following data frame:

      Creature Population
1     Starfish          5
2    Blue Crab          6
3 Bluefin Tuna          4
4   Blue Shark          2
5   Blue Whale          2

Then replace the characters 'Blue' with the characters 'Green':

# substituting the values
sub('Blue','Green',df)

Running this command generates the following output:

Output
"c(\"Starfish\", \"Green Crab\", \"Bluefin Tuna\", \"Blue Shark\", \"Blue Whale\")"
"c(5, 6, 4, 2, 2)"

You can also specify a particular column to replace all the occurrences of 'Blue' with 'Green':

# substituting the values
sub('Blue','Green',df$Creature)

Running this command generates the following output:

Output
"Starfish"
"Green Crab"
"Greenfin Tuna"
"Green Shark"
"Green Whale"

All instances of the characters 'Blue' have been replaced with 'Green'.

The gsub() Function in R

The gsub() function in R is used for replacement operations. The function takes the input and substitutes it against the specified values.

Unlike the sub() function, gsub() applies a global substitution to all matches.

1. Using the gsub() Function

In this example, learn how to substitute a string pattern with a replacement string with the gsub() function.

# the input vector
df<-"In this tutorial, we will install R and show how to add packages from the official Comprehensive R Archive Network (CRAN)."

This is data that has 'R' written multiple times.

# substituting the values using gsub()
gsub('R','The R language',df)

Output
"In this tutorial, we will install The R language and show how to add packages from the official Comprehensive The R language Archive Network (CThe R languageAN)."

All instances of ‘R’ have been replaced (including the instances in "Comprehensive R Archive Network" and "CRAN"). The gsub() function finds every word matching the parameter and replaces that with the input word or values.

2. Using the gsub() Function with Data Frames

The gsub() function also works with data frames.

# creating a data frame
df<-data.frame(Creature=c('Starfish','Blue Crab','Bluefin Tuna','Blue Shark','Blue Whale'),Population=c(5,6,4,2,2))

Let’s prefix the values in the Creature column with 'Deep Sea ':

# substituting the values
gsub('.*^','Deep Sea ',df$Creature)

Running this command generates the following output:

Output
"Deep Sea Starfish"
"Deep Sea Blue Crab"
"Deep Sea Bluefin Tuna"
"Deep Sea Blue Shark"
"Deep Sea Blue Whale"

In this example, the gsub() function uses the regular expression (regex): .*^. This is a pattern for the position at the start of the string.

Conclusion

In this article, you explored how to use sub() and gsub() functions in R. These functions substitute the string or the characters in a vector or a data frame with a specific string. The sub() function applies for the first match. The gsub() function applies for all matches.

Continue your learning with How To Use replace() in R.