how to avoid multiple executions of a impure pipe in angular 2?

Hi I am using Angular 2 pipe to return the keys of object, it is an impure pipe and It is being executed multiple times which is blocking some other script, how can I avoid multiple executions of the impure pipes? my code is as follows :

 import {Pipe,PipeTransform} from '@angular/core';
    @Pipe({ name: 'NgforObjPipe', pure: true })
    export class NgforObjPipe implements PipeTransform {
        transform(value, args:string[]):any {
        let keys = [];
        for (let key in value) {
            keys.push({key: key, value: value[key]});
        }
        console.log('pipeeeeeeeeeeeeeee', keys);
        return keys;
        }
    }