Question

如何在Power BI的M中选择每个类别具有最大值的行。假设我们有表：

+----------+-------+------------+
| Category | Value |    Date    |
+----------+-------+------------+
| apples   |     1 | 2018-07-01 |
| apples   |     2 | 2018-07-02 |
| apples   |     3 | 2018-07-03 |
| bananas  |     7 | 2018-07-04 |
| bananas  |     8 | 2018-07-05 |
| bananas  |     9 | 2018-07-06 |
+----------+-------+------------+

期望的结果是：

+----------+-------+------------+
| Category | Value |    Date    |
+----------+-------+------------+
| apples   |     3 | 2018-07-03 |
| bananas  |     9 | 2018-07-06 |
+----------+-------+------------+

这是PBI的开始表：

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WSiwoyEktVtJRMgRiIwNDC10Dc10DQ6VYHSQ5I2Q5I1Q5Y2Q5Y7BcUmIeEIIkzZElTdAkLZAlTdEkLZElzZRiYwE=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [Category = _t, Value = _t, Date = _t]),
    #"Changed Type" = Table.TransformColumnTypes(Source,{{"Category", type text}, {"Value", Int64.Type}, {"Date", type date}})
in
    #"Changed Type"

我想知道是否有一种方法可以通过添加一些魔术列IsMax在仅一张表中的后续步骤中获得期望的结果：

+----------+-------+------------+-------+
| Category | Value |    Date    | IsMax |
+----------+-------+------------+-------+
| apples   |     1 | 2018-07-01 |     0 |
| apples   |     2 | 2018-07-02 |     0 |
| apples   |     3 | 2018-07-03 |     1 |
| bananas  |     7 | 2018-07-04 |     0 |
| bananas  |     8 | 2018-07-05 |     0 |
| bananas  |     9 | 2018-07-06 |     1 |
+----------+-------+------------+-------+

Answer 1

创建一个计算列：

IsMax =
VAR Max_Value =
    CALCULATE (
        MAX ( Table[Value] ),
        FILTER ( Table, Table[Category] = EARLIER ( Table[Category] ) )
    )
RETURN
    IF ( Table[Value] = Max_Value, 1, 0 )

工作原理：首先，FILTER函数选择表中与当前行具有相同Category的所有记录，并找到它们的最大值。结果保存到变量中。其次，IF比较当前行值和保存的最大值。

Answer 2

在Power Query编辑器中进行基本的分组依据（按Category分组并取Value的最大值）可获得此表：

+----------+-------+
| Category | Value |
+----------+-------+
| apples   |     3 |
| bananas  |     9 |
+----------+-------+

向该表中添加一个自定义列IsMax，该列只是值1，然后将其合并（左外部联接）与在Category和{{1 }}。最后，展开Value列以获取所需的表，但用IsMax代替null。您可以选择替换0的值。

这是所有这些步骤的M代码：

null

Answer 3

我最终通过MAX获得了每个类别的index。这里描述的想法：https://stackoverflow.com/a/51498237/1903793

方法1 是R转换中的单行代码：

library(dplyr)
output <- dataset %>% group_by(Category) %>% mutate(row_no_by_category = row_number(desc(Date)))

方法2 ，完全在PBI中完成：

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("i45WSiwoyEktVtJRMgRiIwNDC10Dc10DQ6VYHSQ5I2Q5I1Q5Y2Q5Y7BcUmIeEIIkzZElTdAkLZAlTdEkLZElzZRiYwE=", BinaryEncoding.Base64), Compression.Deflate)), let _t = ((type text) meta [Serialized.Text = true]) in type table [Category = _t, Value = _t, Date = _t]),
    #"Grouped rows" = Table.Group(Source, {"Category"}, {{"NiceTable", each Table.AddIndexColumn(Table.Sort(_,{{"Date", Order.Descending}} ), "Index",1,1), type table}} ),
    #"Expanded NiceTable" = Table.ExpandTableColumn(#"Grouped rows", "NiceTable", {"Value", "Date", "Index"}, {"Value", "Date", "Index"}),
    #"Filtered Rows" = Table.SelectRows(#"Expanded NiceTable", each ([Index] = 1))
in
    #"Filtered Rows"

选择每个类别具有MAX值的行Power BI

3 个答案: