Making an n-dimensional matrix ruby method

Question

First off, let me say I am new to Ruby and that I heard about NArray but I'd like to see if I can attempt to solve this (with some help from you fine folks)

I learned that I could do something like this:

a=Array.new(2){Array.new(2){Array.new(2,5)}}
=>[[[5, 5], [5, 5]], [[5, 5], [5, 5]]]

from Ruby multidimensional array

I tried to make a generic function like that could take any variables as dimensions, and fill the n dimensional array with a value:

def get_n_dimensional(*args, value)
  myarr= Array.new(args[-1],value)
  args.reverse.drop(1).each{ |arg| myarr=Array.new(arg){myarr}}
  return myarr
end

a = get_n_dimensional(2,2,2,value=5)
puts a.inspect
=> [[[5, 5], [5, 5]], [[5, 5], [5, 5]]]

But I can see how referencing the same array recursively causes problems:

a[0][1][1]=100
puts a.inspect
=> [[[5, 5], [5, 100]], [[5, 5], [5, 100]]]

I'm wondering about other strategies I can use to solve this. I was thinking of perhaps building a string (with looping that depends on the input dimensions) and evaluating it in my function such as:

eval("Array.new(args[0]){Array.new(args[1]){Array.new(args[2],value)}}"

I guess part of my question is if its okay to rely on eval like this

Also this is my first post on SO...let me know if I messed up

Unless I am missing something, I don't think it supports more than 2 dimensions? — Shadesver
– Shadesver, Commented Feb 11, 2017 at 4:06

Cary Swoveland · Accepted Answer · 2017-02-11 04:50:20Z

2

This calls for a recursive method.

def make_nested_array(*dim, v)
  d, *rest = dim
  Array.new(d) { rest.empty? ? v : make_nested_array(*rest, v) }
end

a = make_nested_array(2,3,4,'hi')
  #=> [
  #     [
  #       ["hi", "hi", "hi", "hi"], ["hi", "hi", "hi", "hi"], ["hi", "hi", "hi", "hi"]
  #     ],
  #     [
  #       ["hi", "hi", "hi", "hi"], ["hi", "hi", "hi", "hi"], ["hi", "hi", "hi", "hi"]
  #     ]
  #   ]

To demonstrate no two object_id's are the same, let's change just one element.

a[1,1,1] = 'cat'
a.flatten
  #=> ["hi", "hi", "hi", "hi", "hi", "hi",  "hi", "hi", "hi", "hi", "hi", "hi",
  #    "hi", "hi", "hi", "hi", "hi", "cat", "hi", "hi", "hi", "hi", "hi", "hi"]

edited Feb 11, 2017 at 4:50

answered Feb 11, 2017 at 4:36

Cary Swoveland

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