Converting a Query to a Function in Power Query

You can turn a query into a function by adding a single line before your M query:

() =>

That is a pair of parenthesis ( () ), followed by a goes-to symbol ( => ). Any parameters for your function would go in between the parenthesis.

Example

In the Query Editor, click on the View page, and then click Advanced Editor.

The Advanced Editor will display your M query. Add () => before the starting let statement.

Click Done to return to the Query Editor. You should now see a single Applied Step, and the option to Invoke your function.

Clicking Invoke simply runs your previous query, which isn’t all that interesting. Delete the Invoked step (if you clicked the button), and go back to the Advanced Editor to add a parameter to your function.

Note that when you bring up the editor, it looks a little different …

The code will now look something like this:

let
    Table1 = () =>
let
    Source = Web.Page(Web.Contents("http://boxofficemojo.com/yearly/chart/?page=1&view=releasedate&view2=domestic&yr=2013&p=.htm")),
    Data1 = Source{1}[Data],
    ChangedType = Table.TransformColumnTypes(Data1,{{"Rank", type text}, {"Movie Title (click to view)", type text}, {"Studio", type text}, {"Total Gross /Theaters", type text}, {"Total Gross /Theaters2", type text}, {"Opening /Theaters", type text}, {"Opening /Theaters2", type text}, {"Open", type text}, {"Close", type text}})
in
    ChangedType
in
    Table1

Power Query has automatically prepended some code based on the name of your query. You can remove the outer let statement, or simply ignore it for now. Add a parameter in-between the parenthesis (for example, “page”).

(page) =>
let
    Source = Web.Page(Web.Contents("http://boxofficemojo.com/yearly/chart/?page=1&view=releasedate&view2=domestic&yr=2013&p=.htm")),
    Data1 = Source{1}[Data],
    ChangedType = Table.TransformColumnTypes(Data1,{{"Rank", type text}, {"Movie Title (click to view)", type text}, {"Studio", type text}, {"Total Gross /Theaters", type text}, {"Total Gross /Theaters2", type text}, {"Opening /Theaters", type text}, {"Opening /Theaters2", type text}, {"Open", type text}, {"Close", type text}})
in
    ChangedType

Click Done to return to the editor. Notice that the editor now displays the parameter your entered. It is typed any because we didn’t explicitly specify a type on the parameter.

Clicking Invoke will prompt us for the parameter.

Invoking the query with the parameter doesn’t change our results at all, since we never actually referenced the parameter within our M code… I’ll explain that process in an upcoming post.

Check out the links before for more information on the Power Query Formula Language (“M”):

• Learn about Power Query formulas
• Office help – Library functions
• Deep Dive into Power Query Formula Language (TechEd North America 2014 – Video)