How data reduction algorithm works?

hi everyone,

I have a problem with data reduction algorithm. As I understood from the tutorials, data algorithm works to limit data selection. 

Here is my code in capabilities

"values": {
				"group": {
                "by": "date",
                    "select": [		
						{
                            "bind": {
                                "to": "value1"
                            }
                        },
						{
                            "bind": {
                                "to": "value1_unit"
                            }
                        },
                        {
                            "bind": {
                                "to": "value2"
                            }
                        },{
                            "bind": {
                                "to": "value2_unit"
                            }
                        },
                        {
                            "bind": {
                                "to": "value3"
                            }
                        },{
                            "bind": {
                                "to": "value3_unit"
                            }
                        },
                        {
                            "bind": {
                                "to": "value4"
                            }
                        },{
                            "bind": {
                                "to": "value4_unit"
                            }
                        }

                    ]
					,
					"dataReductionAlgorithm": {
						"bottom": {
						 "count": 1
					 }
					}
					}
                }

By logic, it should group my values by date and select latest, since I'm choosing bottom 1. However, I get all of the data. Where is the problem? Or is there more detailed manual for algorithm.