Reduce/inject for accumulation in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What does the reduce (or inject) method do in Ruby?

It combines all elements of a collection by applying a block or operation, accumulating a single result.

beginner

How do you start an accumulation with a specific initial value using reduce?

Pass the initial value as an argument to reduce, like array.reduce(0) { |sum, n| sum + n }.

beginner

What is the difference between reduce and inject in Ruby?

There is no difference; inject is an alias for reduce.

beginner

Example: What does [1, 2, 3].reduce(:+) return?

It returns 6, the sum of all elements.

intermediate

Can reduce be used to accumulate non-numeric results? Give an example.

Yes. For example, ['a', 'b', 'c'].reduce('') { |acc, s| acc + s } returns 'abc' by joining strings.

What is the purpose of the reduce method in Ruby?

A To create a new array with transformed elements

B To combine all elements of a collection into a single value

C To filter elements based on a condition

D To sort elements in ascending order

reduce combines elements to produce one result, like a sum or product.

How do you specify an initial value for accumulation with reduce?

A By calling <code>initialize</code> method

B By setting a global variable

C By passing it as an argument to <code>reduce</code>

D By using <code>map</code> before <code>reduce</code>

You pass the initial value directly, e.g., reduce(0).

What will [2, 3, 4].reduce(1) { |product, n| product * n } return?

A 9

B None of the above

C 10

D 24

It multiplies all elements starting from 1: 1*2*3*4 = 24.

Which method is an alias for reduce in Ruby?

A inject

B map

C select

D each

inject is exactly the same as reduce.

Can reduce be used to concatenate strings?

A Yes, by accumulating strings

B No, it only works with numbers

C Only if you convert strings to numbers first

D Only with arrays of integers

You can accumulate strings by joining them inside the block.

Explain how reduce works for accumulating values in a Ruby array.

Think about how you add or multiply all elements step by step.

Give an example of using reduce to join an array of strings into one string.

Start with an empty string and add each element.