Problem with identifyBy and displayBy

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**Current behavior**
`// itemsAsObjects = [{display: 0, value: 'Angular'}, {display: 1, value: 'React'}];
`// selectedObjects = [{display: 0, value: 'Angular'}];
<tag-input [ngModel]="selectedItems">
    <tag-input-dropdown [showDropdownIfEmpty]="true"
                        [autocompleteItems]="itemsAsObjects">
    </tag-input-dropdown>
</tag-input>`

See properties of the array and attributes of tag-input element. It works in this way.

**Expected behavior**
`// itemsAsObjects = [{id: 0, name: 'Angular'}, {id: 1, name: 'React'}];
`// selectedObjects = [{id: 0, name: 'Angular'}];
<tag-input [ngModel]="selectedItems" [identifyBy]="'id'" [displayBy]="'name'">
    <tag-input-dropdown [showDropdownIfEmpty]="true"
                        [autocompleteItems]="itemsAsObjects">
    </tag-input-dropdown>
</tag-input>`

It also should work in this way but that error shows up:

> Cannot read property 'toString' of undefined error

**Angular version:** 
Angular 5.2.9

**ngx-chips version:**
1.8.0


**Browser:** [all | Chrome XX | Firefox XX | IE XX | Safari XX | Mobile Chrome XX | Android X.X Web Browser | iOS XX Safari | iOS XX UIWebView | iOS XX WKWebView ]
<!-- All browsers where this could be reproduced -->

[Gbuomprisco]

You need to redefine identifyby and displayby in the dropdown

[oestrada1001]

ngx-chips version: 2.1.0 angular version: 8.2.14

I was getting this error and I was able to get it to work by applying [displayBy] and [identifyBy] to the <tag-input-dropdown> element.

HTML:

...
  <tag-input formControlName="newSkill"
              [identifyBy]="'id'"
              [displayBy]="'keyword'">
    <tag-input-dropdown
        [showDropdownIfEmpty]="true"
        [autocompleteItems]="keywords"
        [identifyBy]="'id'"
        [displayBy]="'keyword'">
    </tag-input-dropdown>
  </tag-input>
...

TS:

...
keywords = [
    [id: 1, keyword: 'art'],
    [id: 2, keyword: 'accounting']
];
...

I used FormBuilder and it’s working properly.