Ruby random array

Question

I have created a two-dimensional (4x4) array, where each element is a random number from -10 to 10.

I would like to now print all negative elements of this array in the terminal. How can one do this?

Here is my code so far which initialises the array, along with my current attempt to print all negative values:

a = Array.new(4) { rand(-10...10) }

a[0] = Array.new(4) { rand(-10...10) }
a[1] = Array.new(4) { rand(-10...10) }
a[2] = Array.new(4) { rand(-10...10) }
a[3] = Array.new(4) { rand(-10...10) }

a.each {|i|
  a.each {|j|
    puts j
  }
}

Your program seems to work fine. What problem are you having? Please ask a specific question. — Hamms
– Hamms, Commented May 24, 2016 at 20:06
Once readers understand the question, someone will be happy to do an edit to help you with the English. Not to worry. I think it's mainly " and when have negative elemt put this elevent in terminal" that we don't understand. — Cary Swoveland
– Cary Swoveland, Commented May 24, 2016 at 20:08
Do you mean you want to display the element (puts ...) if it is negative? If so, do you want to display the element's indices as well (e.g., "a[2,3] = -4")? — Cary Swoveland
– Cary Swoveland, Commented May 24, 2016 at 20:11
rand isn't very random. Use something like: SecureRandom.random_number(-10..10) instead. require 'securerandom' to enable this. — tadman
– tadman, Commented May 24, 2016 at 20:18

Tom Lord · Accepted Answer · 2016-05-24 20:12:12Z

3

You can create the 4x4 array much more simply in a single step, as follows:

a = Array.new(4) { Array.new(4) { rand(-10..10) } }

You can then print all negative values in the 4x4 array via a nested loop:

a.each do |row|
  row.each do |cell|
    puts cell if cell < 0
  end
end

answered May 24, 2016 at 20:12

Tom Lord

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Comments

7urkm3n · Accepted Answer · 2016-05-24 20:50:16Z

1

No need loop it twice.

a = Array.new(4) { Array.new(4) { rand(-10..10) } }

a.flatten.each {|x| puts x if x>0}

answered May 24, 2016 at 20:50

7urkm3n

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1 Comment

Tom Lord Over a year ago

If you want to do more than just puts x, then looping twice is more flexible - for example, you could do each_with_index. In addition, this code is ~2.5 times slower. So yes, your code may be slightly more compact, but it comes at a cost.

Cary Swoveland · Accepted Answer · 2016-05-24 22:54:27Z

1

require 'matrix'

n = 4
m = Matrix.build(n) { rand(-10..10) }
  #=> Matrix[[-5, -8, -3, 7], [-5, 5, 2, 7], [-8, -9, 8, 5], [-2, -9, -2, -4]] 
m.each_with_index { |v,r,c| puts "m[%d,%d] = %d" % [r,c,v] if v < 0 }
m[0,0] = -5
m[0,1] = -8
m[0,2] = -3
m[1,0] = -5
m[2,0] = -8
m[2,1] = -9
m[3,0] = -2
m[3,1] = -9
m[3,2] = -2
m[3,3] = -4

If you wish to return the associated array:

m.to_a
  #=> [[-5, -8, -3, 7], [-5, 5, 2, 7], [-8, -9, 8, 5], [-2, -9, -2, -4]]

edited May 24, 2016 at 22:54

answered May 24, 2016 at 22:37

Cary Swoveland

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