make_bag_if()（聚合函数）make_bag_if() (aggregation function)

• 08/06/2020
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返回组中“Expr”的所有值的 dynamic (JSON) 属性包（字典），其 Predicate 的计算结果为 true。Returns a dynamic (JSON) property-bag (dictionary) of all the values of 'Expr' in the group, for which Predicate evaluates to true.

语法Syntax

summarize make_bag_if(Expr, Predicate [, MaxSize])summarize make_bag_if(Expr, Predicate [, MaxSize])

参数Arguments

• Expr：将用于聚合计算的 dynamic 类型的表达式。Expr: Expression of type dynamic that will be used for aggregation calculation.
• 谓词：必须计算为 true 的谓词，用于将“Expr”添加到结果中。Predicate: Predicate that has to evaluate to true, in order for 'Expr' to be added to the result.
• MaxSize：对返回元素最大数目的可选整数限制（默认值是 1048576）。MaxSize: An optional integer limit on the maximum number of elements returned (default is 1048576). MaxSize 值不能超过 1048576。MaxSize value can't exceed 1048576.

返回Returns

返回组中“Expr”的所有值（属性包（字典））的 dynamic (JSON) 属性包（字典），其 Predicate 的计算结果为 true。Returns a dynamic (JSON) property-bag (dictionary) of all the values of 'Expr' in the group that are property-bags (dictionaries), for which Predicate evaluates to true. 将跳过非字典值。Non-dictionary values will be skipped. 如果一个键出现在多个行中，则会从此键的可能值中选择一个任意值。If a key appears in more than one row, an arbitrary value, out of the possible values for this key, will be selected.

示例Examples

let T = datatable(prop:string, value:string, predicate:bool)
[
    "prop01", "val_a", true,
    "prop02", "val_b", false,
    "prop03", "val_c", true
];
T
| extend p = pack(prop, value)
| summarize dict=make_bag_if(p, predicate)

使用 bag_unpack() 插件将 make_bag_if() 输出中的包键转换为列。Use bag_unpack() plugin for transforming the bag keys in the make_bag_if() output into columns.

let T = datatable(prop:string, value:string, predicate:bool)
[
    "prop01", "val_a", true,
    "prop02", "val_b", false,
    "prop03", "val_c", true
];
T
| extend p = pack(prop, value)
| summarize bag=make_bag_if(p, predicate)
| evaluate bag_unpack(bag)