Custom Angular Material 2 DataTable table header by object

Question

I have a normal Material 2 DataTable, and I want to custom the table header by object

For Example:

      <mat-form-field style="width:100%">
        <input matInput (keyup)="applyFilter($event.target.value)" placeholder="Filter">
      </mat-form-field>

      <div class="mat-elevation-z8">
        <table mat-table [dataSource]="dataSource" matSort>

            <ng-container matColumnDef="{{item}}" *ngFor="let item of old_title_list">
              <th mat-header-cell *matHeaderCellDef mat-sort-header> {{item}} </th>
              <td mat-cell *matCellDef="let row"> {{row[item]}} </td>
            </ng-container>

            <tr mat-header-row *matHeaderRowDef="displayedColumns"></tr>
            <tr mat-row *matRowDef="let row; columns: displayedColumns;">
            </tr>
        </table>

        <mat-paginator [pageSizeOptions]="[5, 10, 25, 100]" [pageSize]="25" showFirstLastButtons></mat-paginator>
    </div>

It successfully display the table, however the th is just presenting the item name defined in data_list object.

So I expect I should change the code to something like below:

         <ng-container matColumnDef="{{item.data}}" *ngFor="let item of new_title_list">
              <th mat-header-cell *matHeaderCellDef mat-sort-header> {{item.title}} </th>
              <td mat-cell *matCellDef="let row">  {{ row[item.data] }} </td>
         </ng-container>

I expect it can get the header value by key but it doesn't. What should I do ?

Sample data:

 var old_title_list = ['aaaaa', '1111', '2222', '3333'];

 var data_list: [{
   aaaaa: 'World',
   '1111': 'this is 1111',
   '2222': 'this is 2222',
   '3333': 'this is 3333',
 },{
   aaaaa: 'World', 
   '1111': 'this is 1111',
   '2222': 'this is 2222',
   '3333': 'this is 3333',
 },{
   aaaaa: 'World',
   '1111': 'this is 1111',
   '2222': 'this is 2222',
   '3333': 'this is 3333',
 }];


var new_title_list = [
    {data: 'aaaaa', title: 'Hello'},
    {data: '1111', title: '1'},
    {data: '2222', title: '2'},
    {data: '3333', title: '3'},
];

Answer 1

You item is object. You must get keys of object by item.keys(), after you can use array of keys to show column name. You can try something like this:

<ng-container matColumnDef="{{item.keys()[i]}}" *ngFor="let item of data_list; let i = index">
              <th mat-header-cell *matHeaderCellDef mat-sort-header> {{item.keys()[i]}} </th>
              <td mat-cell *matCellDef="let row">  {{ (row[item.data] }} </td>
         </ng-container>

if you want use titles from title_list array you can use this code:

<ng-container matColumnDef="{{title_list[i].title}}" *ngFor="let item of data_list; let i = index">
              <th mat-header-cell *matHeaderCellDef mat-sort-header> {{title_list[i].title}} </th>
              <td mat-cell *matCellDef="let row">  {{ (row[item.data] }} </td>
         </ng-container>