Angular2 removing duplicates from an JSON array

问题:

I have a problem with filter in my JSON array when I move my app to Angular2 . In Angular 1.x that was easier. I used 'unique' in filter and this remove all duplicates.

apps:

{"app":"database_1",
 "host":"my_host1",
 "ip":"00.000.00.000"
},
{"app":"database_1",
 "host":"my_host1",
 "ip":"00.000.00.000"
},
{"app":"database_2",
 "host":"my_host2",
 "ip":"00.000.00.000"
},
{"app":"database_2",
 "host":"my_host2",
 "ip":"00.000.00.000"
}

Part of html code:

    <div *ngFor='#appsUnique of apps '>
        <div class="row dashboard-row">
            <div class="col-md-2">
               <h4>{{appsUnique.app }}</h4>
            </div>
        </div>
    </div>

And result is:

database_1
database_1
database_2
database_2

I want to get result:

database_1
database_2

How can I remove duplicates from an array?

回答1:

Mybe it can help you

myList = ["One","two","One","tree"];

myNewList =  Array.from(new Set(myList ));

回答2:

I have a solution for this problem :)

Array.from(new Set([{"app":"database_1",
 "host":"my_host1",
 "ip":"00.000.00.000"
},
{"app":"database_1",
 "host":"my_host1",
 "ip":"00.000.00.000"
},
{"app":"database_2",
 "host":"my_host2",
 "ip":"00.000.00.000"
},
{"app":"database_2",
 "host":"my_host2",
 "ip":"00.000.00.000"
}].map((itemInArray) => itemInArray.app)))

More about Array.from & Set

Thanks all for help :)

回答3:

You could use following method:

names = ["Mike","Matt","Nancy","Adam","Jenny","Nancy","Carl"];

ngOnInit() {
    let filteredNames=this.remove_duplicates(this.names);
    console.log(filteredNames);
    console.log(this.names);
}
remove_duplicates(arr) {
    let obj = {};
    for (let i = 0; i < arr.length; i++) {
        obj[arr[i]] = true;
    }
    arr = [];
    for (let key in obj) {
        arr.push(key);
    }
    return arr;
}

Hope this helps.

回答4:

You could use Observable approach as well, It is very simple.

let filteredData = [];
let arrayData = [{
  "app": "database_1",
  "host": "my_host1",
  "ip": "00.000.00.000"
},
{
  "app": "database_1",
  "host": "my_host1",
  "ip": "00.000.00.000"
},
{
  "app": "database_2",
  "host": "my_host2",
  "ip": "00.000.00.000"
},
{
  "app": "database_2",
  "host": "my_host2",
  "ip": "00.000.00.000"
}];

Observable.merge(arrayData)
  .distinct((x) => x.app)
  .subscribe(y => {
    filteredData.push(y)
    console.log(filteredData)
  });

回答5:

instead of looping over the normal json array, you can create another array in your corresponding typescript class, and alter this as you see fit. In your html, you can then have the following

html

 <div *ngFor='let appsUnique of filteredApps'>
    <div class="row dashboard-row">
        <div class="col-md-2">
           <h4>{{appsUnique.app }}</h4>
        </div>
    </div>
</div>

Next, you need this filteredApps array in your corresponding typescript class.

typescript

 let filteredApps = [];

and in a function you can then create that filteredApps, for example in the onInit method.

onInit()
{
    filteredApps = // filter logic
}

回答6:

You will need trackBy.

Try with:

*ngFor="#appsUnique of posts;trackBy:appsUnique?.app"

Hope it helps.