Array of objects - calculate mean values of properties?

Question

So I have this array of objects

audioFeatures = [
    {danceability: 10, loudness: 2, instrumentalness: 4, energy: 5, acousticness: 7},
    {danceability: 6, loudness: 3, instrumentalness: 8, energy: 9, acousticness: 5},
    {danceability: 7, loudness: 5, instrumentalness: 6, energy: 2, acousticness: 5},
    {danceability: 8, loudness: 10, instrumentalness: 9, energy: 7, acousticness: 2},
]

And I want to calculate a mean value for each property i.e. danceability should = (10+6+7+8)/4 and so on. I have got this working through a plethora of for loops but it seems really inefficient and I ideally want to end up with one object containing each mean value which I haven't figured out.

Does anyone know of a nice way of doing this. I'm coding this in JavaScript but any advise would be appreciated and I can try implement it. I have been trying map but can't quite get my head around how to apply it to this (maybe nested map lol, that's probably not a good idea)

Herohtar · Accepted Answer · 2018-11-08 20:30:14Z

8

You just need two for loops:

audioFeatures = [
    {danceability: 10, loudness: 2, instrumentalness: 4, energy: 5, acousticness: 7},
    {danceability: 6, loudness: 3, instrumentalness: 8, energy: 9, acousticness: 5},
    {danceability: 7, loudness: 5, instrumentalness: 6, energy: 2, acousticness: 5},
    {danceability: 8, loudness: 10, instrumentalness: 9, energy: 7, acousticness: 2},
]

const average = {};

for (const feature of audioFeatures) {
  for (const [key, value] of Object.entries(feature)) {
    if (!average[key]) average[key] = 0;
    average[key] += value / audioFeatures.length;
  }
}

console.log(average);

edited Nov 8, 2018 at 20:30

Herohtar

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answered Nov 8, 2018 at 19:42

Jonas Wilms

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Comments

Nina Scholz · Accepted Answer · 2018-11-08 20:37:15Z

1

You could add the n^th part of the value for the averages by iterating the array and the key/value pairs of the objects.

var audioFeatures = [{ danceability: 10, loudness: 2, instrumentalness: 4, energy: 5, acousticness: 7 }, { danceability: 6, loudness: 3, instrumentalness: 8, energy: 9, acousticness: 5 }, { danceability: 7, loudness: 5, instrumentalness: 6, energy: 2, acousticness: 5 }, { danceability: 8, loudness: 10, instrumentalness: 9, energy: 7, acousticness: 2 }],
    averages = audioFeatures.reduce((result, object, _, { length }) => {
        Object
            .entries(object)
            .forEach(([key, value]) => result[key] = (result[key] || 0) + value / length);
        return result;
    }, Object.create(null));
    
console.log(averages);

.as-console-wrapper { max-height: 100% !important; top: 0; }

edited Nov 8, 2018 at 20:37

answered Nov 8, 2018 at 19:48

Nina Scholz

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7 Comments

Trasiva Over a year ago

Probably because this code is unreadable trying to be "cute".

trincot Over a year ago

@Trasiva, this has nothing to do with "cute", but all with functional programming style.

zfrisch Over a year ago

Destructuring the length directly from the array parameter of reduce and short-circuiting the key to 0 if it doesn't exist are good tricks! Nice job!

Jonas Wilms Over a year ago

I'm still curious to see a real-world codebase written in that style :)

Trasiva Over a year ago

@trincot Go ahead, use code like that in a real work environment. See what your coworkers think of it. That code is not easily readable and self-commenting.

|

Habib Mohammad · Accepted Answer · 2018-11-08 20:35:08Z

0

Try out this one:

var audioFeatures = [
	{danceability: 10, loudness: 2, instrumentalness: 4, energy: 5, acousticness: 7},
	{danceability: 6, loudness: 3, instrumentalness: 8, energy: 9, acousticness: 5},
	{danceability: 7, loudness: 5, instrumentalness: 6, energy: 2, acousticness: 5},
	{danceability: 8, loudness: 10, instrumentalness: 9, energy: 7, acousticness: 2},
];
var meanValues = [];
Object.keys(audioFeatures[0]).forEach(key => {
	console.log(key,
		meanValues[key] = (audioFeatures
			.map(a => a[key])
			.reduce((a, b) => a + b)
			/ audioFeatures.length));
});

Find all keys.
For each key create a map (it will return an array of all values of this key)
Get sum off array using .reduce method.
divide by array length and write it to the variable.

edited Nov 8, 2018 at 20:35

answered Nov 8, 2018 at 20:25

Habib Mohammad

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