CSV library basics in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby CSV code?

Consider this Ruby code using the CSV library. What will it print?

Ruby

require 'csv'
csv_text = "name,age\nAlice,30\nBob,25"
CSV.parse(csv_text, headers: true) do |row|
  puts "#{row['name']} is #{row['age']} years old"
end

A Alice,30\nBob,25

B name is age years old\nAlice is 30 years old

C Alice is 30 years old\nBob is 25 years old

D 30 is Alice years old\n25 is Bob years old

💡 Hint

Look at how CSV.parse with headers:true lets you access columns by name.

The CSV.parse method with headers:true treats the first line as headers. Each row is a CSV::Row object, so row['name'] and row['age'] access the values by column name. The code prints each person's name and age in the given format.

❓ Predict Output

intermediate

What does this Ruby CSV code output?

Given this Ruby code snippet, what will be printed?

Ruby

require 'csv'
csv_text = "id,value\n1,100\n2,200"
rows = CSV.parse(csv_text, headers: true).map { |r| r['value'].to_i * 2 }
puts rows.join(',')

A 100,200

B 200,400

C id,value

D 2,4

💡 Hint

Remember to convert string values to integers before multiplying.

The code parses CSV with headers, extracts the 'value' column as strings, converts them to integers, doubles them, and prints them joined by commas.

🔧 Debug

advanced

Why does this Ruby CSV code raise an error?

This Ruby code raises an error. What is the cause?

Ruby

require 'csv'
csv_text = "name,age\nAlice,30\nBob,25"
CSV.parse(csv_text) do |row|
  puts row['name']
end

A row is an Array, so row['name'] raises TypeError

B CSV.parse requires headers:true to parse correctly

C The CSV library is not required properly

D The CSV text is malformed and missing commas

💡 Hint

Check the type of row when headers option is not set.

Without headers:true, CSV.parse yields each row as an Array, not a CSV::Row. Arrays do not support string keys, so row['name'] raises a TypeError.

📝 Syntax

advanced

Which option correctly reads CSV with headers and prints ages?

Choose the Ruby code snippet that correctly reads CSV text with headers and prints each age.

A CSV.foreach(csv_text) { |row| puts row['age'] }

B CSV.parse(csv_text) { |row| puts row['age'] }

C CSV.read(csv_text, headers: true) { |row| puts row['age'] }

D CSV.parse(csv_text, headers: true) { |row| puts row['age'] }

💡 Hint

Only CSV.parse with headers:true yields rows with string keys.

Option D uses CSV.parse with headers:true, so each row is a CSV::Row and supports row['age']. Option D lacks headers:true, so row is an Array. Option D is invalid because CSV.read does not take a block. Option D expects a filename, not CSV text.

🚀 Application

expert

How many rows are parsed from this CSV string?

Given this Ruby code, how many rows will be parsed and printed?

Ruby

require 'csv'
csv_text = "name,score\nJohn,85\nJane,90\nDoe,78"
rows = CSV.parse(csv_text, headers: true)
puts rows.size

A 3

B 4

C 2

D 1

💡 Hint

Headers are not counted as rows.

The CSV string has one header row and three data rows. CSV.parse with headers:true returns only the data rows, so rows.size is 3.