Angular + Material - How to add custom columns in a table (Mat-Table)

What you are trying to achieve is also made in this package angular4-material-table, which add some structure to allow row insertion, edition and deletion. You have an example to add custom actions columns on this plunkr.

You can define a column with your desired buttons/actions:

<mat-table [dataSource]="dataSource">
    <ng-container matColumnDef="column1"> 
        <mat-header-cell *matHeaderCellDef> column 1 title </mat-header-cell>
        <mat-cell *matCellDef="let row">
            <!-- col 1 -->
        </mat-cell>
    </ng-container> 
    <ng-container matColumnDef="column2"> 
        <mat-header-cell *matHeaderCellDef> column 2 title </mat-header-cell>
        <mat-cell *matCellDef="let row">
            <!-- col 2 -->
        </mat-cell>
    </ng-container>
    <ng-container matColumnDef="actionsColumn">
        <mat-header-cell *matHeaderCellDef>
            <button (click)="createNew()">Create new</button>
        </mat-header-cell>
        <mat-cell *matCellDef="let row">
            <button (click)="edit()">Edit</button>
            <button (click)="cancelOrDelete()">Cancel</button>
        </mat-cell>
    </ng-container>
    <mat-header-row *matHeaderRowDef="displayedColumns">
    </mat-header-row>
    <mat-row *matRowDef="let row; columns: displayedColumns;">
    </mat-row>
</mat-table>

You must include the column in the displayedColumns string array:

displayedColumns = ['column1', 'column2', 'actionsColumn']; 

Here is the one way to do it. It might help someone down the road.

table.html

    <ng-container matColumnDef="action">
       <th mat-header-cell *matHeaderCellDef> Action </th>
       <td mat-cell *matCellDef>
           <ng-container *ngTemplateOutlet="templateRef"></ng-container>
       </td>
   </ng-container>

table.component

 @Input() templateRef: TemplateRef<any>;

table-parent.html

<app-data-table [dataSource]="dataSource" [templateRef]="template">
   <ng-template #template>
      <button mat-icon-button color="warn">
         <mat-icon>delete</mat-icon>
      </button>
      <button mat-icon-button color="primary">
         <mat-icon>edit</mat-icon>
      </button>
   </ng-template>
</app-data-table>

Hope that saves someone couple hours of search :)

On your TableBasicExample.ts add

export class TableBasicExample {
  displayedColumns = ['position', 'name', 'weight', 'symbol', 'customColumn1'];
  dataSource = new ExampleDataSource();
}

And in your html file add the column:

<ng-container matColumnDef="customColumn1">
  <mat-header-cell *matHeaderCellDef> Custom Title</mat-header-cell>
  <mat-cell *matCellDef="let element"> {{element.position}} </mat-cell>
</ng-container>