如何解析高阶图的JSON

Question

我有这个JSON：

var z =   [{
        "signed_up": "2015-08-24T10:31:48.294Z",
        "sessions": 10,
        "browser_family": "Chrome",
        "browser_version": "44.0.2403",
        "timestamp": "2015-08-26T08:36:43.973725Z",
        "useremail": "test@test",
    },
    {
        "signed_up": "2015-08-24T10:31:48.294Z",
        "sessions": 10,
        "browser_family": "Chrome",
        "browser_version": "44.0.2403",
        "timestamp": "2015-08-26T08:36:02.765142Z",
        "useremail": "none",
    },
    {
        "signed_up": "2015-08-25T13:57:00.181Z",
        "sessions": 1,
        "browser_family": "Opera",
        "browser_version": "31.0.1889",
        "timestamp": "2015-08-25T13:57:00.181781Z",
        "useremail": "test1@test",
    },
    {
        "signed_up": "2015-08-24T10:31:48.294Z",
        "sessions": 10,
        "browser_family": "Chrome",
        "browser_version": "44.0.2403",
        "timestamp": "2015-08-25T13:53:43.198419Z",
        "useremail": "none",
    },
    {
        "signed_up": "2015-08-24T10:31:48.294Z",
        "sessions": 10,
        "browser_family": "Chrome",
        "browser_version": "44.0.2403",
        "timestamp": "2015-08-25T07:36:39.891389Z",
        "useremail": "test2@test",
    },
    {
        "signed_up": "2015-08-24T12:58:24.480Z",
        "sessions": 1,
        "browser_family": "Chrome",
        "browser_version": "44.0.2403",
        "timestamp": "2015-08-24T12:58:24.480428Z",
        "useremail": "none",
    }];

http://jsfiddle.net/25xu5xse/3/

如何在“X”行和“Y”行中显示？

我不知道这一切是如何运作的。我尝试使用array[]并在2个不同的数组中推送日期+时间。

对我来说最好的解析看起来像：

[
 ["2015-08-09", "12:33:12"],
]