Adding a property to an array of objects from another array

Question

I have an array like this with names and address:

BTDevices = [
{name:"n1", address:"add1"},
{name:"n2", address:"add2"},
{name:"n3", address:"add3"}]

And another array with alias and address:

EqAlias = [
{btAlias:"a1", address:"add0"},
{btAlias:"a2", address:"add2"},
{btAlias:"a3", address:"add9"}]

I want to add btAlias property to all objects in BTDevices and set the value only if the address are the same, for example in this case I want the following result:

BTDevices:

name:"n1", address:"add1", btAlias:""
name:"n2", address:"add2", btAlias:"a2"
name:"n3", address:"add3", btAlias:""

My first solution was adding btAlias property using forEach and then using two for loops:

// Add Alias
this.BTDevices.forEach(function(obj) { obj.btAlias = "" });

// Set Alias
for (let m = 0; m < this.EqAlias.length; m ++)
{
  for (let n = 0; n < this.BTDevices.length; n++)
  {
    if (this.BTDevices[n].address == this.EqAlias[m].address)
      this.BTDevices[n].btAlias = this.EqAlias[m].btAlias;
  }
}

Is there a better way to do the same? I guess using forEach

Yes you could use forEach, but the finality has no differences. Using forEach might just be more readable that's all. — ChrisR
– ChrisR, Commented Feb 22, 2018 at 16:12

Magus · Accepted Answer · 2018-02-22 16:17:08Z

Using forEach instead of for will just replace the two for loop with forEach. We could argue on which is the best between for and forEach but i don't think there's a good answer. In modern javascript you can also use the for of loop.

Your algorithm is the simpliest and it will work.

But, if you want to address some performances issues, you should want to know that your algorithm is also the slowest (O(n²) complexity)

Another way to do that is to store items of BTDevices in a map to find them faster. Example:

let map = new Map();
BTDevices.forEach(e => map.set(e.address, e));

EqAlias.forEach(e => {
    let device = map.get(e.address);

    if (device) {
        device.btAlias = e.btAlias;
    }
});

The only advantage of this code is that looking for an item in a Map is faster (between O(1) and O(n), it depends of Map implementation). But you won't see any differences unless you try to manipulate some very big arrays.

Eddie · Accepted Answer · 2018-02-22 16:48:32Z

2

You can use map and find

Use map to loop the array and create a new array.

Use find to check if a string is in an array.

let BTDevices = [{name:"n1", address:"add1"},{name:"n2", address:"add2"},{name:"n3", address:"add3"}];
let EqAlias = [{btAlias:"a1", address:"add0"},{btAlias:"a2", address:"add2"},{btAlias:"a3", address:"add9"}];
	
let result = BTDevices.map( v => {
   v.btAlias = ( EqAlias.find( e => e.address == v.address ) || { btAlias:"" } ).btAlias;
   return v;
});
	
console.log( result );

Please check doc: .map, .find

edited Feb 22, 2018 at 16:48

answered Feb 22, 2018 at 16:12

Eddie

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freelancer · Accepted Answer · 2018-02-22 16:32:40Z

1

You could also do something like this.

var BTDevices = [{name:"n1", address:"add1"},{name:"n2", address:"add2"},{name:"n3", address:"add3"}];
var EqAlias = [{btAlias:"a1", address:"add0"},{btAlias:"a2", address:"add2"},{btAlias:"a3", address:"add9"}];
var EqAliasAdd = EqAlias.map((e)=>e.address);
var BTDevicesAdd = BTDevices.map((e)=>e.address);
BTDevicesAdd.map(function(i,k) {
   BTDevices[k].btAlias = "";
   if(EqAliasAdd.indexOf(i) >= 0)
      BTDevices[k].btAlias = EqAlias[k].btAlias;
});
console.log(BTDevices);

answered Feb 22, 2018 at 16:32

freelancer

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