Multidimensional array of zeros in Ruby - ruby

Question

To create a one-dimensional array, I can write:
arr = Array.new(10) { |z| 0 }
#=> [0, 0, 0, 0, 0, 0, 0, 0, 0, 0]
But I want to know how to initialize an array in more dimensions, e.g.:
#=> [[0, 0, 0], [0, 0, 0], [0, 0, 0]]
This is just an example. I am trying to understand the general case.

Answer 1

You can easily nest multiple Array.new calls:
Array.new(2, 0)
#=> [0, 0]
Array.new(3) { Array.new(2, 0) }
#=> [[0, 0], [0, 0], [0, 0]]
Array.new(4) { Array.new(3) { Array.new(2, 0) } }
#=> [[[0, 0], [0, 0], [0, 0]],
# [[0, 0], [0, 0], [0, 0]],
# [[0, 0], [0, 0], [0, 0]],
# [[0, 0], [0, 0], [0, 0]]]
Note that the non-block version, i.e. Array.new(2, 0), should only be used for immutable objects, because the same object will be used for all elements. See the Common gotchas section for details.
To build an array of arbitrary dimensions, you could use recursion:
def multi_array(sizes, default = nil)
size, *remaining = sizes
if remaining.empty?
Array.new(size, default)
else
Array.new(size) { multi_array(remaining, default) }
end
end
multi_array([4, 3, 2], 0)
#=> [[[0, 0], [0, 0], [0, 0]],
# [[0, 0], [0, 0], [0, 0]],
# [[0, 0], [0, 0], [0, 0]],
# [[0, 0], [0, 0], [0, 0]]]

Answer 2

You can also do it like:
Array.new(10, 0).each_slice(2).to_a
# => [[0, 0], [0, 0], [0, 0], [0, 0], [0, 0]]
5.times.map{Array.new(2, 0)}
# => [[0, 0], [0, 0], [0, 0], [0, 0], [0, 0]]

Answer 3

If by more dimensions you mean an array of array, you could try:
arr = Array.new(10){|z| z=Array.new(2,0)}
# => [[0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0,0]]
assuming that your second dimension is 2.

Answer 4

I am trying to understand the general case.
Array.new(n) # where n is natural number 1..n
#=>[nil, nil, nil]
This will create a 1-D Array i:e One dimension array.
Let extends further for a multi-dimensional array i:e Two dimension array .
In ruby, every method accepts a block.
Array.new(3) do
Array.new(3)
end
end
Same can be written In online (macro style) Array.new(3) { Array.new(3) }
[
[nil, nil, nil],
[nil, nil, nil],
[nil, nil, nil]
]
Further, it can extend to initialize each cell value.
Array.new(3) do
Array.new(3) do
0
end
end
[
[0, 0, 0],
[0, 0, 0],
[0, 0, 0]
]
One line micro style Array.new(3) { Array.new(3) { 0 } }
Let extends further three-dimension array.
Array.new(2) do
Array.new(3) do
Array.new(4) do
0
end
end
end
OR
The same can be written as micro-style syntax
Array.new(2) { Array.new(3) { Array.new(4) } {0} }
[
[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]],
[[0, 0, 0, 0], [0, 0, 0, 0], [0, 0, 0, 0]]
]

Answer 5

Here's another way, though I feel the deep copy at every level could somehow be simplified:
def make_multi(dimensions, default)
dimensions.reverse.each_with_index.reduce([]) { |a,(d,i)|
Array.new(d) { i.zero? ? default : Marshal.load(Marshal.dump(a)) } }
end
arr = make_multi [4,3,2,2], 0
#=> [[[[0, 0], [0, 0]], [[0, 0], [0, 0]], [[0, 0], [0, 0]]],
# [[[0, 0], [0, 0]], [[0, 0], [0, 0]], [[0, 0], [0, 0]]],
# [[[0, 0], [0, 0]], [[0, 0], [0, 0]], [[0, 0], [0, 0]]],
# [[[0, 0], [0, 0]], [[0, 0], [0, 0]], [[0, 0], [0, 0]]]]
arr[0][0][0][0] = 1
arr
#=> [[[[1, 0], [0, 0]], [[0, 0], [0, 0]], [[0, 0], [0, 0]]],
# [[[0, 0], [0, 0]], [[0, 0], [0, 0]], [[0, 0], [0, 0]]],
# [[[0, 0], [0, 0]], [[0, 0], [0, 0]], [[0, 0], [0, 0]]],
# [[[0, 0], [0, 0]], [[0, 0], [0, 0]], [[0, 0], [0, 0]]]]
arr = make_multi [4,3,2,2], {}
#=> [[[[{}, {}], [{}, {}]], [[{}, {}], [{}, {}]], [[{}, {}], [{}, {}]]],
# [[[{}, {}], [{}, {}]], [[{}, {}], [{}, {}]], [[{}, {}], [{}, {}]]],
# [[[{}, {}], [{}, {}]], [[{}, {}], [{}, {}]], [[{}, {}], [{}, {}]]],
# [[[{}, {}], [{}, {}]], [[{}, {}], [{}, {}]], [[{}, {}], [{}, {}]]]]
arr[0][0][0][0] = { a: 1 }
arr
#=> [[[[{:a=>1}, {}...] # all but the first are empty hashes

Answer 6

Try it:)
arr = Array.new(10, 0)
UPD: for multidimensional is:
arr = Array.new(10, Array.new(2, 0))
=> [[0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0], [0, 0]]