I use this item for a loop of all columns in Columns, the index is not working for the array iterator value. How do I get this to work?

<ng-container matColumnDef= "{{columnName}}" *ngFor=" let columnName of Columns; index as i"> <th mat-header-cell *matHeaderCellDef>{{columnName == 'Expand' ? '' : columnName}} <td mat-cell *matCellDef="let data">{{data.Days[i][columnName]}}

data.Days is an array RROR TypeError: Cannot read properties of undefined (reading ''