Ruby 2D Array ExamplesUse 2D arrays and jagged arrays. Nest arrays and access subarrays.
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.
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|
# End of row.
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 = 
# Add first row.
# Create second row.
subarray = 
# Add second row.
# Load an element.
puts "Third element in first row is: " << String(values)
# Change this element.
values = 500
# Display all elements.
values.each do |x|
x.each do |y|
Third element in first row is: 3
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]
0 0... A
0 1... B
0 2... C
1 0... D
1 1... E
1 2... F
2 0... G
2 1... H
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]]
# Call flatten to change a 2D array into one dimension.
[["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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