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javascriptjqueryarrays
sir_thursday
sir_thursday

Reputation: 5409

JavaScript combining two dimensional arrays

Let's say I have two arrays:

var a = [[1, 10], [2, 10], [3, 10], [4, 10], [5, 10]];
var b = [[1, 20], [3, 20], [4, 20]];

I want to combine these two into a new array:

var c = [[1, 10, 20], [2, 10], [3, 10, 20], [4, 10, 20], [5, 10]];

What's the best way to go about doing this. I'll update my question in a second with what I've tried to do.

var c = [];
for(var i = 0; i < a.length; i++) {
  for(var j = 0; j < b.length; j++) {
    if(a[i][0] == b[j][0]) {
      // Push b value into a
      a[i][0].push(b[j][1]);
    } else {
      // Don't do anything...
    }
  }
}

c = a;  // Useless code here but just wanted to return c
return c;

Upvotes: 0

Views: 541

Answers (2)

JakeSidSmith
JakeSidSmith

Reputation: 933

Example

var a = [[1, 10], [2, 10], [3, 10], [4, 10], [5, 10]];
var b = [[1, 20], [3, 20], [4, 20]];
var c = [];

// Loop over a
for (var n = 0; n < a.length; n++) {
    // Create copy of a's value
    var subA = a[n].slice(0);
    // Loop over b
    for (var i = 0; i < b.length; i++) {
        var subB = b[i];
        // Check if a contains b
        if (subA.indexOf(subB[0]) === 0) {
            // Add b to new a value
            subA.push(subB[1]);
        }
    }
    // Add new value to c
    c.push(subA);
}

console.log(a)
console.log(c);

Edit 1: updated for loop

Edit 2: If first item equals first item

Edit 3: Slice a to retain original values

Upvotes: 2

Bergi
Bergi

Reputation: 664346

Why don't you use plain arrays? They can be sparse.

var a = [10, 10, 10, 10, 10];
var b = [20,   , 20, 20];

Now get them into one array:

var c = new Array(Math.max(a.length, b.length));
for (var i=0; i<c.length; i++)
    if (i in a && i in b)
        c[i] = [a[i], b[i]];
    else if (i in a)
        c[i] = [a[i]];
    else if (i in b)
        c[i] = [b[i]];

For the case that your objects (the items really don't have to be arrays) consist of a non-integer indexing values, you might use a simple standard merge algorithm on the two sorted lists. It will run in O(n+m), not in O(n*m) as your solution. See this answer for an example implementation and further pointers.

Upvotes: 1

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