javascript: switch elements of each element in multidimensional array

Question

I have a multidimensinal array containing a list of pairs of coordinates:

var coordinates = [
[
    16.383223226146004,
    48.21122334186088
],
[
    16.384753966103307,
    48.211128793925674
],
[
    16.384923422642906,
    48.211127770652936
],
[
    16.38575514277135,
    48.21122830416087
]...

What is the most performant option to switch the coordinate pairs around for all the entries in the array. The list of coordinates can be very long, so I'm looking for a fast working solution.

Expected result:

coordinates = [
[
    48.21122334186088,
    16.383223226146004
],
[
    48.211128793925674,
    16.384753966103307
],
[
    48.211127770652936
    16.384923422642906,
],
[
    48.21122830416087,
    16.38575514277135
]...

The most performant option probably is to change the access-methods/-indizes. — Sirko
– Sirko, Commented Aug 3, 2014 at 16:46

Mritunjay · Accepted Answer · 2014-08-03 16:53:48Z

3

Use Array reverse function

coordinates.forEach(function (coordinate) {
    coordinate.reverse();
})

edited Aug 3, 2014 at 16:53

answered Aug 3, 2014 at 16:47

Mritunjay

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1 Comment

Sirko Over a year ago

You don't need the coordinate = here as reverse() is in-place.

adeneo · Accepted Answer · 2014-08-03 17:49:37Z

2

What is the most performant option to switch the coordinate pairs around for all the entries in the array!

Generally speaking the fastest is usually the simplest, regular loops and just setting the array indices

for (var i=coordinates.length; i--;) {
    var temp = coordinates[i][0];
    coordinates[i][0] = coordinates[i][1];
    coordinates[i][1] = temp;
}

Here's a JSPerf to test different methods

http://jsperf.com/switch-elements

It's about 95% faster than forEach and reverse

jsperf

That's a huge difference, while this code changes the indices in an array with 1000 arrays almost 500k times, the code using forEach and reverse, only executes 17k times.

edited Aug 3, 2014 at 17:49

answered Aug 3, 2014 at 16:48

adeneo

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3 Comments

aidanjacobson Over a year ago

You can do [coordinates[i][0], coordinates[i][1]] = [coordinates[i][1], coordinates[i][0]] to achieve the same switching effect. Not sure about the efficiency, though.

adeneo Over a year ago

@Awesomeness01 - Yes, today destructuring is an option, Back in 2014 it wasn't.

aidanjacobson Over a year ago

Oops, didn't see the date, my bad. So used to it that it seems like it always was this way.

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