initialize array of arrays in ruby [duplicate]

Question

When we initialize an array of arrays using

ar = Array.new(2, [0, -1])

It creates an array which looks like [[0, -1], [0, -1]]

But when we change the value in the inner array, it gets reflected in all elements of the array.

ar[0][0] = 5
puts ar

[[5, -1], [5, -1]]

Seems the same object is getting inserted into each index of the outer array. What is the correct way to prevent this?

John Ledbetter · Accepted Answer · 2021-03-18 20:37:30Z

1

Use the Array.new block form:

ar = Array.new(2) { [0, -1] }

Since the array literal [0, -1] is scoped to the block, a new instance is created on every invocation. You can test this by adding a puts or similar in the block:

ar = Array.new(2) { |n| puts "called for element #{n}"; [0, -1] }

results in:

called for element 0
called for element 1
=> [[0, -1], [0, -1]]

answered Mar 18, 2021 at 20:37

John Ledbetter

14.3k1 gold badge65 silver badges82 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

initialize array of arrays in ruby [duplicate]

1 Answer 1

Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Linked

Related