Sort first array based on second array issue

Question

I am trying to sort a JavaScript array based on sort order in a second array. I have already gone through other similar questions here in SO and came up with the below code. Be the output is not getting as expected.

var legends = ["Maths","Physics","English","French","Chemistry"];
var sortOrder = [1,400,300,200,-3];

legends.sort( function (a, b) {
    return sortOrder[legends.indexOf(a)] >= sortOrder[legends.indexOf(b)];   
  });


console.log(legends);

The desired output is

["Chemistry", "Maths", "French", "English", "Physics"];

Chemistry denotes the sort order -3
Maths next higher count, that is 1
French next higher count, that is 200

I am trying to get the desired output either in pure JS or using D3js, not sure if I am doing it right!

Francesco · Accepted Answer · 2018-06-08 07:01:17Z

3

You are almost right but in the sort function, you refer to legends array which is being mutated, so indexes does not match to original order.

To demonstrate that this is the case, you could copy the array and sort the copy:

var legends = ["Maths","Physics","English","French","Chemistry"];
var legendsToSort = ["Maths","Physics","English","French","Chemistry"];

var sortOrder = [1,400,300,200,-3];

legendsToSort.sort( function (a, b) {
    return sortOrder[legends.indexOf(a)] >= sortOrder[legends.indexOf(b)];   
  });


console.log(legendsToSort);

answered Jun 8, 2018 at 7:01

Francesco

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5 Comments

Nina Scholz Over a year ago

very funny. just to mention a possible drawback of this.

Francesco Over a year ago

not being funny here, I thank you for pointing out this problem. I just wanted to help OP understand why his method wasn't working, not to give a better solution

FinitePixels Over a year ago

@Francesco sort values are not unique, it can be like [1,5,5,4,-3] and legends will be unique as it will be plotted in a graph. But the point as you mentioned is, my array array was getting mutated.

FinitePixels Over a year ago

@NinaScholz its a good point, but my legends array will not have duplicates.

FinitePixels Over a year ago

Accepted the answer, but unable to upvote due to low reputation ;(

Nina Scholz · Accepted Answer · 2018-06-08 07:12:45Z

3

You could take a helper array with indices, sort them and map the wanted array.

var legends = ["Maths", "Physics", "English", "French", "Chemistry"],
    sortOrder = [1, 400, 300, 200, -3];

legends = [...legends.keys()]
    .sort((a, b) => sortOrder[a] - sortOrder[b])
    .map(i => legends[i]);        

console.log(legends);

edited Jun 8, 2018 at 7:12

answered Jun 8, 2018 at 7:01

Nina Scholz

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1 Comment

FinitePixels Over a year ago

It helped, wish I could upvote, but unable due to low reputation, new here ;)

Nikhil Aggarwal · Accepted Answer · 2018-06-08 07:09:06Z

1

Try following

var legends = ["Maths","Physics","English","French","Chemistry"];
var sortOrder = [1,400,300,200,-3];

/* Create an array of objects of value index of sortOrder */
legends = Object.entries(sortOrder.reduce((a,v,i) => Object.assign(a, {[v]:i}), {}))
.sort((a,b) => a[0] - b[0]) // Sort array based on sortOrder values
.map(([s, i]) => legends[i]); // fetch items from legends based on sorted order 

console.log(legends);

answered Jun 8, 2018 at 7:09

Nikhil Aggarwal

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1 Comment

FinitePixels Over a year ago

Thanks for your time, wish I could upvote, but unable due to low reputation, new here ;)

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