sub and gsub in R Programming - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the sub() function do in R?

sub() replaces the first occurrence of a pattern in a string with a replacement.

beginner

How is gsub() different from sub()?

gsub() replaces all occurrences of a pattern in a string, while sub() replaces only the first.

beginner

Example: What is the output of sub("a", "X", "banana")?

The output is "bXnana" because only the first 'a' is replaced by 'X'.

beginner

Example: What is the output of gsub("a", "X", "banana")?

The output is "bXnXnX" because all 'a's are replaced by 'X'.

intermediate

Can sub() and gsub() work with regular expressions?

Yes, both functions use regular expressions to find patterns in strings for replacement.

What does sub("cat", "dog", "catapult") return?

A "dogapult"

B "catapult"

C "dogdog"

D "catdog"

sub() replaces the first occurrence of "cat" with "dog", so "catapult" becomes "dogapult".

Which function replaces all matches of a pattern in a string?

A sub()

B gsub()

C paste()

D strsplit()

gsub() replaces all occurrences of the pattern, unlike sub() which replaces only the first.

What will gsub("[aeiou]", "*", "hello world") output?

A "h*ll* w*rld"

B "hello world"

C "h*llo world"

D "*e*o *o*l*"

All vowels (a, e, i, o, u) are replaced by '*', so "hello world" becomes "h*ll* w*rld".

If you want to replace only the first space in a string, which function do you use?

A gsub()

B str_replace_all()

C sub()

D paste()

sub() replaces only the first match, so it is used to replace the first space.

What is the role of regular expressions in sub() and gsub()?

A They convert strings to numbers

B They replace the string directly

C They split the string

D They define the pattern to find in the string

Regular expressions define the pattern that sub() and gsub() look for to replace.

Explain the difference between sub() and gsub() in R.

Think about how many replacements each function makes.

Describe a real-life example where you would use gsub() instead of sub().

Imagine editing a whole paragraph, not just one word.