Custom function basic syntax in M language (Power Query)
This is about the custom functions in Power Query.
In an example, we will create a new column (New Price) from current one (Price), adding 1. (Yes, this can be done in Power Query without custom function, but I need very simple example...)
Function written directly in query
Function can be written in a query, which uses it. At the beginning, or whenever before its call.
- let
MyFunction = (OldPrice as number) =>
OldPrice + 1,
Source = Excel.Workbook(File.Contents("C:\Users\cars.xlsx"), null, true),
Sheet = Source{[Item="Sheet1",Kind="Sheet"]}[Data],
Headers = Table.PromoteHeaders(Sheet, [PromoteAllScalars=true]),
Types = Table.TransformColumnTypes(Headers,{{"Price", type number}}),
Call_Function = Table.AddColumn(Types, "New price", each MyFunction([Price]), type number)
in
Call_Function
Separate function called from query
We need function:
- let
MyFunction = (OldPrice as number) =>
OldPrice + 1
in
MyFunction
- let
Source = Excel.Workbook(File.Contents("C:\cars.xlsx"), null, true),
Sheet1_Sheet = Source{[Item="Sheet1",Kind="Sheet"]}[Data],
Headers = Table.PromoteHeaders(Sheet1_Sheet, [PromoteAllScalars=true]),
Types = Table.TransformColumnTypes(Headers,{{"Brand", type text}, {"Model", type any}, {"Price", Int64.Type}, {"Color", type text}, {"On Stock from:", type date}}),
#"Invoked Custom Function" = Table.AddColumn(Types, "New price", each function([Price]))
in
#"Invoked Custom Function"