JavaScript - Separate array into an array of pairs

Question

I have an array of team names which is like this:

teams = ['team1', 'team2', 'team3', 'team4']

I want to create a set of matches based on this, so at the moment, for a set of matches using the teams array you would get:

teamMatches : [
  [ teams[0],  teams[1] ],
  [ teams[2],  teams[3] ]
]

My question is, can anyone think of a way to produce this teamMatches array based upon a teams array with length n. The teams array will always be a correct number, 4,8,16 etc. I have tried using Math.pow with 2 to try to produce the brackets with no success.

Any ideas?

georg · Accepted Answer · 2013-04-12 11:57:36Z

3

A procedural solution:

xs = [0,1,2,3,4,5,6,7,8,9]
result = []
n = 2 // n=3 gives a list of triples, etc
for(var i = 0; i < xs.length; i += n)
    result.push(xs.slice(i, i + n))

A functional programming solution:

function zip() {
    var args = [].slice.call(arguments, 0);
    return args[0].map(function(_, n) {
        return args.map(function(a) {return a[n] })
    })
}

xs = [0,1,2,3,4,5,6,7,8,9]
result = zip(
    xs.filter(function(_, n) { return n % 2 == 0 }),
    xs.filter(function(_, n) { return n % 2 != 0 })
)
// [[0,1],[2,3],[4,5],[6,7],[8,9]]

Explanation: zip is a function (built-in in some programming languages, but not in Javascript) that takes N arrays and groups together elements at the same position:

zip([1,2,3], [10,20,30]) -> [ [1,10], [2,20], [3,30] ]

We split an array into even and odd parts:

[0,2,4,6...]
[1,3,5,7...]

and zip them together, getting a list of ordered pairs.

edited Apr 12, 2013 at 11:57

answered Apr 12, 2013 at 11:41

georg

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4 Comments

Μenelaοs Over a year ago

shouldn't it be javascript though?

georg Over a year ago

@meewoK: eh? this is javascript.

Μenelaοs Over a year ago

Ah..you implemented Zip function in javascript. Nice one.

georg Over a year ago

@alex23: by convention, _ denotes unused/ignored parameters, a kind of placeholder.

Gowsikan · Accepted Answer · 2013-04-12 11:48:47Z

1

How about this

var teams = ['team1', 'team2', 'team3', 'team4'];
var teamMatches = new Array();
for(var i=0;i<teams.length; i+=2)
{       
  teamMatches.push([teams[i],teams[i+1]]);
}

answered Apr 12, 2013 at 11:48

Gowsikan

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2 Comments

germainelol Over a year ago

I like this due to its simplicity so thanks, didn't think the answer was as simple as this so maybe I was overthinking it. This should work for an array of size 4/8/16 etc as well shouldn't it?

Μenelaοs Over a year ago

This is great. The question was actually much simpler than everyone thought at first. The questioner was not looking for some over complex round robit, etc algorithm.

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