data.table（R）中按组的频率表

Question

我想为每个组获取因子/分类变量值的频率。

以下不起作用：

Error in `[.data.table`(dt, , list(table(fac)), by = grp) : 
  All items in j=list(...) should be atomic vectors or lists. If you are trying something like j=list(.SD,newcol=mean(colA)) then use := by group instead (much quicker), or cbind or merge afterwards.

错误消息是：

Sub Example1_ForLoop()

    Dim lastRow As Long, x As Long
    Dim Criteria1 As Variant, Criteria2 As Variant

    Criteria1 = 2134
    Criteria2 = "003"

    lastRow = Range("A" & Rows.Count).End(xlUp).Row

    For x = 1 To lastRow
        If Cells(x, 1) = Criteria1 And Cells(x, 2) = Criteria2 Then

            Cells(x, 6) = Cells(x, 3)

        End If

    Next

End Sub


Sub Example2_ForEachLoop()

    Dim c As Range, SearchRange As Range
    Dim Criteria1 As Variant, Criteria2 As Variant

    Criteria1 = 2134
    Criteria2 = "003"

    Set SearchRange = Range("A1", Range("A" & Rows.Count).End(xlUp))

    For Each c In SearchRange
        If c = Criteria1 And c.Offset(0, 1) = Criteria2 Then

            c.Offset(0, 5) = c.Offset(0, 3)

        End If

    Next

End Sub

'Here is the proper way to use Find and FindNext.

Sub Example3_DoLoop_Find_FindNext()

    Dim c As Range, SearchRange As Range
    Dim firstAddress As String
    Dim Criteria1 As Variant, Criteria2 As Variant

    Criteria1 = 2134
    Criteria2 = "003"

    Set SearchRange = Range("A1", Range("A" & Rows.Count).End(xlUp))

    Set c = SearchRange.Find(Criteria1, LookIn:=xlValues)

    If Not c Is Nothing Then
        firstAddress = c.Address
        Do

            If c = Criteria1 And c.Offset(0, 1) = Criteria2 Then

                c.Offset(0, 5) = c.Offset(0, 3)

            End If

            Set c = SearchRange.FindNext(c)
        Loop While Not c Is Nothing And c.Address <> firstAddress
    End If

End Sub

有没有简单的方法来完成这项任务？感谢。

Answer 1

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dcast