这个例子将展示如何在groovy中按值对Map或Dictionary进行排序。如果你有一个域，一个键和值的表，你可能想用描述的顺序来显示一个下拉菜单。如果你不能通过数据库排序，一个直接的方法是按值对Map进行排序。我从gmail中提取了一些用于邮件操作的样本值。

我们将使用groovy spaceship operator。对于按值反向排序的map，我们只需切换我们要比较的内容。

按值排序

@Test
void sort_map_by_value() {
    def myMap = [1:"More", 2:"Mark as read", 3: "Mark as important", 4:"Add to tasks"]
    assert [
        "Add to tasks",
        "Mark as important",
        "Mark as read",
        "More"] == myMap.sort({a, b -> a.value <=> b.value})*.value
}

Map反向排序

@Test
void sort_map_by_value_reverse() {
    def myMap = [1:"More", 2:"Mark as read", 3: "Mark as important", 4:"Add to tasks"]
    assert [
        "More",
        "Mark as read",
        "Mark as important",
        "Add to tasks"] == myMap.sort({a, b -> b.value <=> a.value})*.value
}

按值排序，不区分大小写

@Test
void sort_map_by_value_case_insensitive() {
    def myMap = [1:"More", 2:"Mark as read", 3: "Mark as important", 4:"Add to tasks"]
    assert [
        "Add to tasks",
        "Mark as important",
        "Mark as read",
        "More"] == myMap.sort({a, b -> a.value.toLowerCase() <=> b.value.toLowerCase()})*.value
}