Angular-FormArray: Creating a table form from 2-dimensional Javascript array

I need to create a table form with Angular which is based on a simple 2-dimensional array of arrays.
The data structure is simple but the data in the cells is interdependent. The single cells are accessed by indices alone e.g., row:1, col:0.
Custom validators need to be defined on on cell-level. In addition, there may be validators for rows and columns.

I tried various ways to define FormArray holding an array of FormControls. But I am unsure how to access the respective FormControl by row and column indices alone in the Angular template.

Model

[
  ['a', 'b'],
  ['c', 'd']
]

FormGroup

  form = new FormGroup({
    rows: new FormArray([...])
  });

Expected result

I am tried various things similar to this:

  <form [formGroup]="form"">
    <div formArrayName="rows">
      <div 
        *ngFor="let row of rows.controls; let rowIndex = index" [formGroupName]="rowIndex">
        <div formArrayName="cols">
          <div
            *ngFor="let col of form.get('cols').controls; let colIndex = index"
            [formGroupName]="colIndex">
            <input [formControlName]="colIndex" />
          </div>
        </div>
      </div>
    </div>
  </form>

Solution

Dabbel, if you has an Array of Array, create a FormArrays of FormArrays (sorry for the joke)

Well, imagine you has data=[ ['a', 'b'], ['c', 'd'] ]

You can in ngOnInit create the formArray of FormArray like

//At firs a empty FormArray
this.formArray = new FormArray([]);
//with each element of data
this.data.forEach(x => {
  //x is e.g.['a','b']
  //we create a emptt FormArray
  const obj = new FormArray([]);
  //add a FormControl
  x.forEach(y => {
    obj.push(new FormControl(y));
  });
  //and push in the formArray
  this.formArray.push(obj);
});

or abreviated using map like

this.formArray=new FormArray(
  this.data.map(x=>new FormArray(
    x.map(y=>new FormControl(y))))
)

Well, How mannage a FormArray outside a FormGroup? If our FormArray is a FormArray of FormGroup, we make in general

 <!--yes we can use [formGroup] with a FormArray-->
<form [formGroup]="formArray">
   <!--iterate over the formArray.controls, that is a formGroup-->
  <div *ngFor="let group of formArray.controls;let i=index">
     <div [formGroup]="group">
       <input formControlName="name">
        ...
     </div>
  </div>
</form>

Well, our formArray is a FormArray of FormArray, but remember that we using [formGroup] with an array and iterate over formArray.controls.

<form [formGroup]="formArray">
    <div *ngFor="let subarray of formArray.controls;let i=index">
        <div [formGroup]="subarray">
            <ng-container *ngFor="let control of subarray.controls;let j=index">
                <input [formControl]="control">{{control.invalid?"*":""}}
       </ng-container>
        </div>
    </div>
</form>

NOTE: I use <ng-container> nor <div> to not create addicionals divs. (We can not put the *ngFor in the own input because, then, we can not have access to control.invalid

Well, as you want create Validators, we are changing a bit when we create the formGroup to include the validators, I put a "fool" example

this.formArray=new FormArray(
  this.data.map(x=>new FormArray(
    x.map(y=>new FormControl(y,Validators.required)),
    this.rowValidator())),this.arrayValidator()
)

And ours validators can be like

  rowValidator()
  {
    return (array:FormArray)=> {
      const invalid:boolean=array.value.
             filter((x,index)=>array.value.indexOf(x)!=index).length>0
      return invalid?{error:'must be different'}:null
    }
  }
  arrayValidator()
  {
      return (array:FormArray)=> {
        let arrayJoin="";
        array.value.forEach(x=>arrayJoin+=x.join(''))
        return arrayJoin=="abcd"?null:{error:'must be a,b,c,d'}
      }
  }

You can see in the stackblitz

NOTE: In a real application, we neen't use so many Validators. Take account the cost of this validator on the perfomance of the app