sub and gsub in R Programming - Step-by-Step Execution

Concept Flow - sub and gsub

Input String

↓

Apply Pattern Match

↓

sub: Replace first match only

→Output String

↓

gsub: Replace all matches

→Output String

The flow shows how sub replaces only the first pattern match in a string, while gsub replaces all matches.

Execution Sample

R Programming

text <- "apple apple apple"
sub("apple", "orange", text)
gsub("apple", "orange", text)

Replace 'apple' with 'orange' once using sub, and all occurrences using gsub.

Execution Table

Step	Function	Input String	Pattern	Replacement	Result
1	sub	"apple apple apple"	"apple"	"orange"	"orange apple apple"
2	gsub	"apple apple apple"	"apple"	"orange"	"orange orange orange"

💡 Both functions finish after replacing matches; sub replaces only the first, gsub replaces all.

Variable Tracker

Variable	Start	After sub	After gsub
text	"apple apple apple"	"apple apple apple"	"apple apple apple"
result_sub	NA	"orange apple apple"	NA
result_gsub	NA	NA	"orange orange orange"

Key Moments - 2 Insights

Why does sub only replace the first 'apple' and not the others?

sub stops after the first match and replaces it, as shown in execution_table row 1 where only the first 'apple' changes.

Does gsub change the original string variable?

No, gsub returns a new string with all replacements; the original 'text' variable remains unchanged as shown in variable_tracker.

Visual Quiz - 3 Questions

Look at the execution_table, what is the result of sub at step 1?

A "orange apple apple"

B "apple orange apple"

C "orange orange orange"

D "apple apple apple"

💡 Hint

Check the 'Result' column in execution_table row 1.

At which step does the function replace all occurrences of 'apple'?

A Step 1

B Step 2

C Neither step

D Both steps

💡 Hint

Look at the 'Function' and 'Result' columns in execution_table.

If we assign the result of gsub to 'text', what will variable_tracker show after gsub?

A "apple apple apple"

B "orange apple apple"

C "orange orange orange"

D NA

💡 Hint

Refer to variable_tracker row for 'result_gsub' and imagine assigning it back to 'text'.

Concept Snapshot

sub(pattern, replacement, x) replaces only the first match in x.
gsub(pattern, replacement, x) replaces all matches in x.
Both return a new string; original string stays unchanged unless reassigned.
Use sub for single replacement, gsub for global replacement.

Full Transcript

In R, sub and gsub are functions to replace text patterns in strings. sub replaces only the first occurrence of the pattern, while gsub replaces all occurrences. For example, given the string 'apple apple apple', sub("apple", "orange", text) changes only the first 'apple' to 'orange', resulting in 'orange apple apple'. gsub("apple", "orange", text) changes all 'apple' words to 'orange', resulting in 'orange orange orange'. Neither function changes the original string unless you assign the result back to the variable. This visual trace shows each step and how variables change, helping beginners understand the difference clearly.