Forum Discussion

p45cal's avatar
p45cal
Icon for Solution Supplier rankSolution Supplier
1 year ago
Solved

The 'right' way to bring a custom function requiring arguments 'inline'

I have a table to which I want to add a column listing dates 1 month apart for the duration: So for the second row I want to generate:   Note that this question is not asking abou...
Need Help
  • AlienSx's avatar
    AlienSx
    1 year ago

    p45cal , regarding "in-line" function definition and call: consider Function.Invoke as an alternative. Example: 

     

    ( ) => 5 // this is our function
( ( ) => 5 )( ) // this is how you call it now
Function.Invoke( ( ) => 5, { } ) // alternative way to call our function

     

    I am not aware of any other alternatives. And there is nothing wrong with your current approach. But the fact that you apply it to solve that particular problem (the one with different "_" conflicting each other) does not look like a ... reasonable one in that particular case. The problem is solved by different identifiers, not by "in-line function call".

     

AlienSx's avatar
AlienSx
Icon for Super User rankSuper User
1 year ago

p45cal the problem with your 1st code is with a "context" you are referring to in List.Generate. Try to replace "each" with (argument_name) => like I did it here: 

 

let
    Source = Table.FromRows(Json.Document(Binary.Decompress(Binary.FromText("JcfBDQAgCASwXe5NwglidBbC/msosb9mgkO51GgOgb9EZ6IkMbby/AroSusEqi4=", BinaryEncoding.Base64), Compression.Deflate)),{"Start Date","End Date"}),
    ChangedType = Table.TransformColumnTypes(Source,{{"Start Date", type date}, {"End Date", type date}},"en-GB"),
    Custom1 = Table.AddColumn(
        ChangedType, 
        "ListMonths", 
        (row) => List.Generate(
            () => row[Start Date], 
            (x) => x <= row[End Date], 
            (x) => Date.AddMonths(x, 1)
        )
    )
in
    Custom1

 

Now it's clear that Start Date and End Date belong to ChangeType table, not List.Generate function. At the same time I replaced "each" in List.Generate with (x) =>. This function works now because List.Generate knows that "row" belongs to the current row (record) of ChangedType table. I would recommend you to forget about "each" for some time. Use (x) => , (y) => , (w) => - whatever you like to use but not each (aka (_) =>)

p.s. read this article written by Ben Gribaudo about identifier scope