Iterate pairwise through a ruby array [duplicate]

Question

How can i iterate over a ruby array and always get two values, the current and the next, like:

[1,2,3,4,5,6].pairwise do |a,b|
  # a=1, b=2 in first iteration
  # a=2, b=3 in second iteration
  # a=3, b=4 in third iteration
  # ...
  # a=5, b=6 in last iteration
end

My usecase: I want to test if an array is sorted, and by having an iterator like this i could always compare two values.

I am not searching for each_slice like in this question: Converting ruby array to array of consecutive pairs

Stefan · Accepted Answer · 2016-06-22 12:35:16Z

55

You are looking for each_cons:

(1..6).each_cons(2) { |a, b| p a: a, b: b }
# {:a=>1, :b=>2}
# {:a=>2, :b=>3}
# {:a=>3, :b=>4}
# {:a=>4, :b=>5}
# {:a=>5, :b=>6}

edited Jun 22, 2016 at 12:35

Stefan

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answered Jun 22, 2016 at 12:06

Ursus

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2 Comments

Andi Over a year ago

Yes, this is exactly what i need! I looked through Enumerable and Enumerator but did not see this one. Thx

Stefan Over a year ago

@Andi and regarding your use case: ary.each_cons(2).all? { |a, b| a <= b } returns true if the values are sorted. (unfortunately, you can't use all?(&:<=) here due to the way each_cons yields values)

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