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Ruby 2D Array ExamplesUse 2D arrays and jagged arrays. Nest arrays and access subarrays.
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2D array. Often data is two-dimensional. We need to access cells by rows and columns. With the Array in Ruby, we can nest Arrays, creating 2D arrays.

With nested iterators, we loop over elements. And with built-in methods like flatten() we can transform nested arrays into 1-dimensional ones.

First example. Here we use an Array initialization statement to create a 2D array in one line. We then use the each iterator to loop over rows.

Finally We invoke the each iterator to process the individual cells in the nested arrays.

Ruby program that uses 2D array
# This 2D array contains two sub-arrays. values = Array[[10, 20, 30], [40, 50, 60]] # Loop over each row array. values.each do |x| # Loop over each cell in the row. x.each do |cell| puts cell end # End of row. puts "--" end
10 20 30 -- 40 50 60 --

Push. Here we create nested Arrays with push method calls. We create an empty Array and then create a subarray. We add three elements to it with push().

Lookup We can look up the element in a 2D array by accessing first the row and then the column of the cell.

Ruby program that uses 2D array, push
values = [] # Create first row. subarray = [] subarray.push(1) subarray.push(2) subarray.push(3) # Add first row. values.push(subarray) # Create second row. subarray = [] subarray.push(10) subarray.push(20) subarray.push(30) # Add second row. values.push(subarray) # Load an element. puts "Third element in first row is: " << String(values[0][2]) # Change this element. values[1][1] = 500 # Display all elements. values.each do |x| x.each do |y| puts y end puts "--" end
Third element in first row is: 3 1 2 3 -- 10 500 30 --

Indexes. Next we show how to access each cell in a 2D array by indexes. We use the each_index iterator on rows, and then call it again on each row.

Coordinates We then access each cell value using the two coordinates from the iterators.

Tip This style of code also handles uneven, jagged arrays—we get a different maximum row index for each row.

Ruby program that uses each_index
# This is an irregular 2D array (a jagged array). values = [["A", "B", "C"], ["D", "E", "F"], ["G", "H"]] # Loop over indexes. values.each_index do |i| # Get subarray and loop over its indexes also. subarray = values[i] subarray.each_index do |x| # Display the cell. puts String(i) << " " << String(x) << "... " << values[i][x] end end
0 0... A 0 1... B 0 2... C 1 0... D 1 1... E 1 2... F 2 0... G 2 1... H

Flatten. A 2D array has depth. A flat array is one-dimensional. With flatten, and "flatten!" we convert a multidimensional array into a flat one.

Tip This method works recursively. Even heavily nested arrays (3-dimensional, 4-dimensional ones) are flattened.

Ruby program that uses flatten method
gems = [["ruby", 10], ["sapphire", 20]] p gems # Call flatten to change a 2D array into one dimension. gems.flatten! p gems
[["ruby", 10], ["sapphire", 20]] ["ruby", 10, "sapphire", 20]

A summary. In Ruby we compose two-dimensional arrays by nesting Arrays. This also gives us the ability to create jagged (uneven) arrays.

Features. With each and each_index, we iterate over nested collections. With flatten, we have a method that changes nested arrays into linear ones.

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