PC-coding/programming-univbasics-nds-nested-arrays-iteration-lab-part-3-nyc01-seng-ft-060120

Nested Data Structures: Reducing Data

For the final lab on traversing Array of Arrays, we're going to apply the double while loop to find a single value.

Traverse Array of Arrays to Produce a Single Value

Another variant on traversing nested Arrays is traversing the matrix and accumulating all the values. Let's imagine that someone created a grid representing a guessing game. In each cell of the grid, the games makers have put some amount of cash. Let's sum up all the possible values to determine how much money is in the grid.

guessing_game_grid = [
 [1, 2, 1, 7, 3],
 [2, 100, 15, 4, 18],
 [15, 16, 99, 1, 2, 11]
]

total = 0
row_index = 0
while row_index < guessing_game_grid.count do
  element_index = 0
  while element_index < guessing_game_grid[row_index].count do
    total += guessing_game_grid[row_index][element_index]
    element_index += 1
  end
  row_index += 1
end
total #=> 297

This pattern is known as reduction because you're going to reduce a nested data structure to a single value. As you learn Ruby's Enumerable methods, remembering this name will help a lot!

Instructions

In this lab, you'll be working with a mix of data types - nested arrays with strings and numbers. We need to extract out the strings from this data, ignoring the numbers.

Write a method, join_nested_strings, that can take in an array of arrays of integers and strings. This method should iterate over each nested array, combining all the strings into a single string value.

For example, given the code below:

mixed_data = [
  ["The", 4, "quick"],
  [-1, "brown", "fox", 30],
  ["studied", 101, 233, "Ruby"]
]

join_nested_strings(mixed_data)

We should expect the following returned:

"The quick brown fox studied Ruby"

Note: Don't worry if your resulting string has an extra space at the end - the tests will ignore it.

Conclusion

We've seen examples of methods like .join that combine arrays of strings, but in this situation, we need something more customizable. We were able to take a set of 'dirty' data and reduce it down to a single value, something that .join would not be able to accomplish on its own.

You may have noticed that when we're discussing nested data structures - a lot of the concepts we are introducing are things we've seen in regular arrays. At the core of our implementations, we're performing operations that we're familiar with - using conditional statements, combining values, pushing data into arrays, etc... We're incorporating these basic tasks with loops to produce custom data tools.