JS 数组根据属性实现类似sql的group by 分组

			groupBy = function ( array , f ) {
			    var groups = {};
			    array.forEach( function( o ) {
			        var group = JSON.stringify( f(o) );
			        groups[group] = groups[group] || [];
			        groups[group].push( o );
			    });
			    return Object.keys(groups).map( function( group ) {
			        return groups[group];
			    });
			}
			var  newFetchData = groupBy(fetchData, function(item){
			    return [要分组的属性];
			});