Multi-Dimensional Arrays

Earlier we learned that arrays can store any type of value. If that is true, can we store arrays inside of arrays? Well yes we can….

A multi-dimensional array is an array of arrays, meaning that the values inside the array are also arrays. The inner arrays can store other values such as strings, numbers, or even more arrays.

The figure below demonstrates a synonyms array that has arrays as values. The inner arrays contain words that are synonyms of each other. Notice each inner array has an index position.

Two Dimensional Arrays

The simplest form of a multi-dimensional array is a two dimensional array. A two dimensional array is like a spreadsheet with rows and columns. To access items in a two dimensional array, use square bracket notation and two indexes array[0][0]. The first index is for the outer array, or the “row”, and second index is for the inner array, or the “column”.

let shuttleCrews = [
    ['Robert Gibson', 'Mark Lee', 'Mae Jemison'],
    ['Kent Rominger', 'Ellen Ochoa', 'Bernard Harris'],
    ['Eilen Collins', 'Winston Scott',  'Catherin Coleman']
];

console.log(shuttleCrews[0][2]);
console.log(shuttleCrews[1][1]);
console.log(shuttleCrews[2][1]);

Mae Jemison
Ellen Ochoa
Winston Scott

Multi-Dimensions and Array Methods

In a multi-dimensional array, both the inner and outer arrays can be altered with array methods. However, bracket notation must be used correctly.

To apply a method to the outer array, the syntax is:

multiArrayName.method();

To apply a method to one of the inner arrays, the syntax is:

multiArrayName[indexOfInnerArray].method();

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let shuttleCrews = [
    ['Robert Gibson', 'Mark Lee', 'Mae Jemison'],
    ['Kent Rominger', 'Ellen Ochoa', 'Bernard Harris'],
    ['Eilen Collins', 'Winston Scott',  'Catherin Coleman']
];

let newCrew = ['Mark Polansky', 'Robert Curbeam', 'Joan Higginbotham'];

// Add a new crew array to the end of shuttleCrews
shuttleCrews.push(newCrew);
console.log(shuttleCrews[3][2]);

// Reverse the order of the crew at index 1
shuttleCrews[1].reverse();
console.log(shuttleCrews[1]);

Joan Higginbotham
[ 'Bernard Harris', 'Ellen Ochoa', 'Kent Rominger' ]

Beyond Two Dimensional Arrays

Generally, there is no limit to how many dimensions you can have when creating arrays. However it is rare that you will use more than two dimensions. Later on in the class we will learn about more collection types that can handle complex problems beyond the scope of two dimensional arrays.

Check Your Understanding

let school = [
    ["science", "computer", "art"],
    ["Jones", "Willoughby", "Rhodes"]
];