Php 从数组中获取最低值并删除重复项

我需要： 1.获取[id_vehicle]的最低值[alert] 2.删除[id_车辆]的副本 3.按[id\U车辆]对数组进行排序

因此，在这种情况下，最低值为2016-03-07。我该怎么做？这是我的阵列：

Array
    (
        [0] => stdClass Object
            (
                [id] => 2
                [id_vehicle] => 35
                [remind] => 2016-03-07
                [alert] => 2016-10-09
            )

        [1] => stdClass Object
            (
                [id] => 3
                [id_vehicle] => 35
                [remind] => 2016-05-02
                [alert] => 2016-03-07
            )

        [2] => stdClass Object
            (
                [id] => 4
                [id_vehicle] => 35
                [remind] => 2016-08-01
                [alert] => 2016-05-02
            )

        [3] => stdClass Object
            (
                [id] => 5
                [id_vehicle] => 35
                [remind] => 2016-11-07
                [alert] => 2016-08-01
            )

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到目前为止你试过什么？给我们看一些代码，我不知道怎么做。我想我需要一些foreach函数或usort？