Question

I need to know how you break an array into sub-arrays based on the value of the integers in the array. What I’m trying to do is take a large array and break it into 1-10, 11-20, 21-30…etc and I need to then be able to count those sub arrays so I have numbers that are like “7 integers between 1-10, 6 integers between 11-20, 12 integers between 21-30.”

I’ve got a single line random number generator that will give me my array like the following:

rand_num = (Array.new(200) {(1..100).to_a[rand(100)]})

This gives me my array of 200 hundred random numbers between 1 and 100 and now I need to be able to split them apart according to value and tell how much is in each one.

Then I need it to display those numbers. I’ve searched everywhere and I want to say you do this with .partition, but I just can’t get it to work.

Answer 1

If your buckets really are that simple then you could use group_by like this:

array.group_by { |n| (n - 1) / 10 }

That will give you Hash like this:

{0=>[1, 2, 3, ...], 1=>[11, 12, 13, ...], ...}

then you just throw in a sort_by to force a nice ordering and a map to summarize the results:

array.group_by { |n| (n - 1) / 10 }.
      sort_by { |k, v| k }.
      map { |n, a| [10 * n + 1 .. 10 * (n + 1), a.length] }

For example:

# The %7 is just an easy way to get a non-uniform set.
>> (1..100).select { |n| n % 7 == 0 }
=> [7, 14, 21, 28, 35, 42, 49, 56, 63, 70, 77, 84, 91, 98]
>> (1..100).select { |n| n % 7 == 0 }.sort_by { |k, v| k }.group_by { |n| (n - 1) / 10 }.map { |n, a| [10 * n + 1 .. 10 * (n + 1), a.length] }
=> [[1..10, 1], [11..20, 1], [21..30, 2], [31..40, 1], [41..50, 2], [51..60, 1], [61..70, 2], [71..80, 1], [81..90, 1], [91..100, 2]]