/**
 * @param items {array} - array from which to remove duplicates
 * @param test {function} - function that returns the desired "index" from which to base duplication
 * @return {array} - a duplicate free items
 *
 * @example
 * const peeps = [{name:"bob"},{name:"pat"},{name:"pat"},{name:"bob"}];
 * removeDuplicates( peeps, item => item.name );
 * // [{name:"bob"},{name:"pat"}];
 */
function removeDuplicates( items, test ){
  const indexes = [];
  return items.reduce( (p,c)=>{
    const acc = p;
    if( indexes.indexOf( test.call(this, c) ) === -1 ) {
        indexes.push( test.call( this, c ) );
        acc.push( c );
        return acc;
    }
    return p;
  },[]);
}