Multidimensional array in javasscript

Question

I'm learning from the book JavaScript for Dummies, and from the following code, it says

console.log( bestAlbumsByGenre[0][1] ) //will output: Patsy Cline:Sentimentally Yours

var bestAlbumsByGenre = []
bestAlbumsByGenre[0] = “Country”;
bestAlbumsByGenre[0][0] = “Johnny Cash: Live at Folsom Prison”
bestAlbumsByGenre[0][1] = “Patsy Cline: Sentimentally Yours”;
bestAlbumsByGenre[0][2] = “Hank Williams: I’ m Blue Inside”;

but in the console the output is: "o". Why is that, and what am I doing wrong?

That code does not make any sense. [0][0] would be a string and it is acting like it is an array. The line should be `bestAlbumsByGenre[0] = [];` — epascarello, Sep 18 '18 at 14:36
It really doesn't, you are setting a character of a String to a String, where is that in Js for Dummies? — Luca Kiebel, Sep 18 '18 at 14:37
I've added your code to a snippet. Click Run code snippet and you'll see the errors. — Heretic Monkey, Sep 18 '18 at 14:37
@PatrickRoberts I see nothing in the question that indicates it's pseudo-code. Can you point out where that is mentioned? — Heretic Monkey, Sep 18 '18 at 14:39
If you replaced the `= "Country";` in the second line with `= [];`, it will do what you likely want. This at least is an actual multidimensional array. — Scott Sauyet, Sep 18 '18 at 14:42
Possible duplicate of [Declare an empty two-dimensional array in Javascript?](https://stackoverflow.com/questions/18163234/declare-an-empty-two-dimensional-array-in-javascript) — serge, Sep 18 '18 at 15:34

dschu · Accepted Answer · 2018-09-18T14:54:07.710

You seem to have mixed up two different exercises. The following line is resulting in the error:

bestAlbumsByGenre[0] = "Country";

I've cleaned up the code to make it work.

However, I think I would prefer an object, where each key represents the genre, and their value is an array.

// Define the outer array
const bestAlbumsByGenre = [];

// Set the first element of the array as an array
bestAlbumsByGenre[0] = [];

// Add items to the first element (the array)
bestAlbumsByGenre[0][0] = "Johnny Cash: Live at Folsom Prison"
bestAlbumsByGenre[0][1] = "Patsy Cline: Sentimentally Yours";
bestAlbumsByGenre[0][2] = "Frank Williams: I’ m Blue Inside";

console.log(bestAlbumsByGenre[0][1]);

// Alternative approach
const reallyBestAlbumsByGenre = {
    rock: [],
};

reallyBestAlbumsByGenre.rock.push("Johnny Cash: Live at Folsom Prison");
reallyBestAlbumsByGenre.rock.push("Patsy Cline: Sentimentally Yours");
reallyBestAlbumsByGenre.rock.push("Frank Williams: I’ m Blue Inside");

console.log( reallyBestAlbumsByGenre.rock[1] );

This is by far the most thorough example. It shows how to fix the problem for the exercise using a 2D array as well as explains how to do it with an object. — Code-Apprentice, Sep 18 '18 at 16:35

score 0 · Answer 2 · edited Sep 18 '18 at 15:31

0

Your not actually accessing a two dimensional array, but you are accessing the second character of a string.

Your are initializing a 1 dimensional array of string when you do:

When you did the following:

var bestAlbumsByGenre = [];
bestAlbumsByGenre[0] = "Country";

You assigned a string to the first element.

Subsequently, the other statements did nothing.

Fix

The following fixes your error:"

var bestAlbumsByGenre = [[]]
bestAlbumsByGenre[0][0] = "Country";

edited Sep 18 '18 at 15:31

serge

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answered Sep 18 '18 at 14:41

Menelaos

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yup, so how can i access, lets say: [country] [Johnny Cash..] from the mentioned code – Mattey Sep 18 '18 at 14:44
@Mattey `var bestAlbumsByGenre = [[]]` , `bestAlbumsByGenre[0][0] = "Country";` – Menelaos Sep 18 '18 at 14:45
it does thanks, but can i access some inner elements within the array, maybe: bestAlbumsByGenre[0][1] //“Patsy Cline: Sentimentally Yours”; is there a way to do it – Mattey Sep 18 '18 at 14:49
@Maltey: did you try it? – Scott Sauyet Sep 18 '18 at 14:50
Wouldn't it be better in this case to separate the creation of the outer array from the creation of the inner one? It's odd if you then add the "Jazz" category and have to add that specifically to the outer array, but magically the initial "Country" one was there. So I would do `var bestAlbumsByGenre = []` followed by `bestAlbumsByGenre[0] = []`. It certainly seems a better approach for teaching beginners. – Scott Sauyet Sep 18 '18 at 14:56
@ScottSauyet, it does work, thanks a lot. think I need to keep on learning about arrays and Objects. – Mattey Sep 18 '18 at 15:18

Code-Apprentice · Answer 3 · 2018-09-18T14:53:49.597

0

Since you want to organize albums by genre, it would make more sense to create an object with the genre as a key:

var bestAlbumsByGenre = {
    "Country": [
        "Johnny Cash: Live at Folsom Prison",
        "Patsy Cline: Sentimentally Yours",
        "Hank Williams: I’m Blue Inside",
    ]
}

edited Sep 18 '18 at 14:53

answered Sep 18 '18 at 14:50

Code-Apprentice

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This is certainly correct. But the OP mentioned that this was an attempt to understand an example in a beginners' book. – Scott Sauyet Sep 18 '18 at 14:51
Thanks a lot, hav a gud day. – Mattey Sep 18 '18 at 14:54
2

agree with @ScottSauyet, I'll add that the exercise is about arrays[], not about objects{} – serge Sep 18 '18 at 15:12

Multidimensional array in javasscript

3 Answers3

Fix