Split and join methods in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the split method do in Ruby?

The split method breaks a string into an array of smaller strings based on a separator you provide. If no separator is given, it splits on whitespace by default.

beginner

How does the join method work in Ruby?

The join method takes an array of strings and combines them into one string, inserting a separator between each element if you provide one.

beginner

Example: What is the result of "apple,banana,carrot".split(",")?

It returns the array ["apple", "banana", "carrot"] by splitting the string at each comma.

beginner

Example: What does ["red", "green", "blue"].join("-") return?

It returns the string "red-green-blue" by joining the array elements with a dash between them.

intermediate

Why are split and join useful together?

You can use split to break a string into parts, change or process those parts, then use join to put them back together into a new string.

What is the default separator for the split method in Ruby if none is provided?

A Comma

B Period

C Whitespace (spaces, tabs, newlines)

D No separator, returns whole string in array

If you don't give a separator, split divides the string at whitespace by default.

What will "one two three".split return?

A Error

B ["one two three"]

C ["o", "n", "e"]

D ["one", "two", "three"]

Without an argument, split splits on spaces, so it returns an array of words.

What does ["a", "b", "c"].join return?

A "a,b,c"

B "abc"

C "a b c"

D Error

Without a separator, join combines elements directly with no spaces.

Which method would you use to turn a string into an array?

A split

B join

C map

D select

split breaks a string into an array based on a separator.

Which method would you use to combine an array of strings into one string?

A join

B split

C reduce

D flatten

join combines array elements into a single string.

Explain how you can use split and join together to change a sentence.

Think about breaking a sentence into words, changing words, then making a new sentence.

Describe what happens when you call split without any arguments on a string.

What does Ruby consider whitespace?

Practice

1. What does the Ruby method split do when called on a string?

easy

A. It divides the string into an array based on a separator.

B. It combines array elements into a single string.

C. It changes all characters to uppercase.

D. It removes spaces from the string.

Solution

1. Step 1: Understand the purpose of split

   The split method breaks a string into parts wherever a separator is found.

2. Step 2: Identify the output type

   After splitting, the output is an array containing the separated parts of the string.

3. Final Answer:

   It divides the string into an array based on a separator. -> Option A

4. Quick Check:

   split = divide string into array [OK]

Hint: Split cuts strings into arrays at separators [OK]

Common Mistakes:

• Thinking split joins array elements
• Confusing split with uppercase conversion
• Assuming split removes spaces without separator

2. Which of the following is the correct syntax to join an array ["a", "b", "c"] into a string separated by dashes in Ruby?

easy

A. ["a", "b", "c"].split("-")

B. ["a", "b", "c"].join("-")

C. "a-b-c".join(["a", "b", "c"])

D. "a-b-c".split(["a", "b", "c"])

Solution

1. Step 1: Identify the method to combine array elements

   The join method is used on arrays to create a string with a separator.

2. Step 2: Check the syntax for join with a separator

   The syntax is array.join(separator), so ["a", "b", "c"].join("-") is correct.

3. Final Answer:

   ["a", "b", "c"].join("-") -> Option B

4. Quick Check:

   join(array) with separator = correct syntax [OK]

Hint: Use array.join(separator) to combine elements [OK]

Common Mistakes:

• Using split instead of join to combine
• Calling join on a string instead of array
• Passing array as argument to split or join incorrectly

3. What is the output of this Ruby code?

sentence = "apple,banana,cherry"
fruits = sentence.split(",")
result = fruits.join(" & ")
puts result

medium

A. apple & banana & cherry

B. apple,banana,cherry

C. apple banana cherry

D. ["apple", "banana", "cherry"]

Solution

1. Step 1: Split the string by commas

   The split(",") breaks the string into ["apple", "banana", "cherry"].

2. Step 2: Join the array with " & " separator

   The join(" & ") combines the array elements into the string "apple & banana & cherry".

3. Final Answer:

   apple & banana & cherry -> Option A

4. Quick Check:

   split then join with & = apple & banana & cherry [OK]

Hint: Split by comma, join with & gives 'apple & banana & cherry' [OK]

Common Mistakes:

• Expecting original string without changes
• Confusing split and join order
• Thinking join adds commas automatically

4. The following Ruby code is intended to split a string into words and then join them with a space, but it raises an error. What is the problem?

text = "hello world"
words = text.split
joined = words.join
puts joined()

medium

A. The variable words is not an array.

B. The method split requires an argument.

C. The call joined() is incorrect syntax.

D. The join method cannot be called without a separator.

Solution

1. Step 1: Check the method calls

   split without arguments splits on whitespace correctly. join can be called without arguments to join with empty string.

2. Step 2: Identify the error in puts joined()

   In Ruby, calling a variable like a method with parentheses joined() causes an error because joined is a string, not a method.

3. Final Answer:

   The call joined() is incorrect syntax. -> Option C

4. Quick Check:

   Calling string like method with () = error [OK]

Hint: Don't add () when printing variables in Ruby [OK]

Common Mistakes:

• Thinking split needs an argument always
• Assuming join requires a separator
• Calling variables as methods with parentheses

5. Given a string data = "red;green;blue;yellow", write Ruby code to split it into an array, remove the color "blue", and then join the remaining colors with commas. What is the correct output?

hard

A. "red;green;yellow"

B. "red,green,blue,yellow"

C. "red green yellow"

D. "red,green,yellow"

Solution

1. Step 1: Split the string by semicolons

   Using split(";") on data gives ["red", "green", "blue", "yellow"].

2. Step 2: Remove "blue" from the array

   Remove "blue" by using array.delete("blue") or array.reject!.

3. Step 3: Join the remaining elements with commas

   Joining with join(",") results in "red,green,yellow".

4. Final Answer:

   "red,green,yellow" -> Option D

5. Quick Check:

   Split by ;, remove blue, join by , = red,green,yellow [OK]

Hint: Split by ; remove item, join by , for final string [OK]

Common Mistakes:

• Forgetting to remove "blue" before joining
• Joining with wrong separator
• Using split without argument or wrong separator