[Solved] Select consecutive integers from array in Ruby [closed]

Question

Your code compares adjacent elements x and y, but pushes x and y only if they are the first elements in the array (if z == 0; newarray.insert(0, x, y)). Otherwise, only y is pushed, so the first element of each group of consecutive integers is missing.

This table illustrates what’s going on:

  x   y   y == x+1
--------------------
  1   3   false
  3   6   false
  6   7   true      #=> push(7)
  7   8   true      #=> push(8)
  8   9   true      #=> push(9)
  9  10   true      #=> push(10)
 10  12   false
 12  13   true      #=> push(13)
 13  17   false

You could fix your code by using z as an indicator for the beginning of a group:

z = true
array.sort.each_cons(2) do |x, y|
  if y == x + 1
    if z
      newarray.push(x, y)
      z = false
    else
      newarray.push(y)
    end
  else
    z = true
  end
end

A better way is to use chunk_while that was introduced in Ruby 2.3:

array = [1, 3, 9, 6, 7, 10, 8, 12, 13, 17]

array
  .sort                              #=> [1, 3, 6, 7, 8, 9, 10, 12, 13, 17]
  .chunk_while { |x, y| y == x + 1 } #=> [[1], [3], [6, 7, 8, 9, 10], [12, 13], [17]]
  .select { |a| a.size > 1 }         #=> [[6, 7, 8, 9, 10], [12, 13]]
  .flatten                           #=> [6, 7, 8, 9, 10, 12, 13]

Did you notice that the documentation contains a similar example?

For example, one-by-one increasing subsequence can be chunked as follows:
a = [1,2,4,9,10,11,12,15,16,19,20,21]
b = a.chunk_while {|i, j| i+1 == j }
p b.to_a #=> [[1, 2], [4], [9, 10, 11, 12], [15, 16], [19, 20, 21]]

Accepted Answer