Setting values of multidimensional arrays

Ruby
1

Hi!

I have a problem where I have to set values in a multidimensional array
with a range of dimensions.

My function gets two arguments. First the array to set, and second an
array with indexes.

Lets say indexes are [1,2,3,4,5] and the name of the array is “arr”. I
then want to set the value of arr[1][2][3][4][5]. How can I achive this?

I was thinking about a loop with pointers/references but that doesn’t
seem to exist in ruby? Are there other solutions?

2

You can assign the array to variable, and then hand that variable to
each step in the loop. The loop goes through the indices and updates the
variable, drilling down progressively through the layers.
By using an “each” loop, you don’t need to know how deep the array goes.
You can then handle as many layers as necessary.

a = Array.new(8) { Array.new(8) { Array.new(8) { Array.new(8) {
Array.new(8,1) } } } }

a[1][2][3][4][5] = 2

def test( array, indices )
indices.each { |idx| array = array[idx] }
array
end

test a, [1,2,3,4,5]
=> 2

3

I’m sorry if I didn’t make myself very clear in my first post but while
that works great for retrieving the value of the multidimensional array,
my problem is setting the value.

Like

a = Array.new(8) { Array.new(8) { Array.new(8) { Array.new(8) {
Array.new(8,1) } } } }

a[1][2][3][4][5] = 2

def test( array, indices )
#Something equivalent of array[1][2][3][4][5] = 10
end

test a, [1,2,3,4,5] => #Modified array

4

Sorry if I didn’t understand well but maybe you can make two loops.

something like this

a = Array.new(8) { … }
indexes = [1,2,3,4,5]

a.each do
indexes.each do |i|
ar[i] = …
end
end

for each index read you set that right position of array with some value

5

Very Newbe wrote in post #1143808:

I’m sorry if I didn’t make myself very clear in my first post but while
that works great for retrieving the value of the multidimensional array,
my problem is setting the value.

Like

a = Array.new(8) { Array.new(8) { Array.new(8) { Array.new(8) {
Array.new(8,1) } } } }

a[1][2][3][4][5] = 2

def test( array, indices )

It seems there is an argument missing for the new value.

#Something equivalent of array[1][2][3][4][5] = 10
end

test a, [1,2,3,4,5] => #Modified array

like

def update(array, indices, value)
(indices[0…-1].inject(array) {|a,i| a[i]})[indices.last] = value
end

?

Cheers

robert

6

Robert K. wrote in post #1143822:

It seems there is an argument missing for the new value.

like

def update(array, indices, value)
(indices[0…-1].inject(array) {|a,i| a[i]})[indices.last] = value
end

?

Cheers

robert
Exactly! Wow that was a really neat solution, got to love ruby. :slight_smile:

Thanks a lot for the replies

7

Wender J. wrote in post #1143810:

Sorry if I didn’t understand well but maybe you can make two loops.

something like this

a = Array.new(8) { … }
indexes = [1,2,3,4,5]

a.each do

There is absolutely no point in the line above. Iterating the root
Array does not make sense.

indexes.each do |i|
ar[i] = …
end
end

for each index read you set that right position of array with some value

Cheers

robert

8

Robert K. wrote in post #1143822:

def update(array, indices, value)
(indices[0…-1].inject(array) {|a,i| a[i]})[indices.last] = value
end

Dammit… I live for the day when I can offer solutions as elegant as
Robert’s!