Question

下面，我需要返回一个带有Category属性的值的独特列表。

<root>
    <classifications>
        <classification name="Category">Category One</classification>
        <classification name="Sub-Category">Sub-Category One</classification>
    </classifications>
    <classifications>
        <classification name="Category">Category Two</classification>
        <classification name="Sub-Category">Sub-Category One</classification>
    </classifications>
    <classifications>
        <classification name="Category">Category One</classification>
        <classification name="Sub-Category">Sub-Category Two</classification>
    </classifications>
    <classifications>
        <classification name="Category">Category Three</classification>
        <classification name="Sub-Category">Sub-Category One</classification>
    </classifications>
    <classifications>
        <classification name="Category">Category One</classification>
        <classification name="Sub-Category">Sub-Category Two</classification>
    </classifications>
    <classifications>
        <classification name="Category">Category Two</classification>
        <classification name="Sub-Category">Sub-Category One</classification>
    </classifications>
</root>

使用classifications/classification[@name="Category"]我得到：

Category One
Category Two
Category One
Category Three
Category One
Category Two

我需要的是：

Category One
Category Two
Category Three

Answer 1

此XPath将选择不同的元素：

//classification[@name = "Category" and not(preceding::classification = .)]

或更具体：

//classification[@name = "Category" 
    and not(preceding::classification[@name = "Category"] = .)
]

Answer 2

对于那些能够使用XPath 2.0及更高版本的人：

另一种可能更灵活，效率更高的替代方法（至少在Saxon 9.8.0中）是：

distinct-values(//classification[@name = 'Category'])

XPath按属性过滤并返回不同的值

2 个答案: