Facing issue with while binding property through filter results?

Ionic Framework ionic-v3
1 
<div *ngIf="cateogorywiseofferdatawithsearchTags.length>0">
  <p>....Related Offers...</p>
</div>

<div class="stackofcardswithsearch" *ngIf="searchContent">
  <div *ngFor=" let item of ( cateogorywiseofferdatawithsearchTags | offersfilter: selectedcategory )">

</div>
</div>

I have different tabs based on that i am filtering the data but the problem is I am filtering the data based on original data but changes or affecting to dummy data.

suppose if i send original=[1,2,3] ,I am taking dummy array dummy=[1,2,3] i am returning the values based on that suppose dummy=[1] I need to show related offers text based on this dummy array length how can i do that?