Table.ColumnNames returns Text or List?

[absherzad]

Hi everyone,
I am confused if Table.ColumnNames() returns the output as Text or List?
The documentation says it returns Text as demonstrated below, but the output looks like a List to me.

Table.ColumnNames(table as table) as {Text}

 

[Ozeroth]

Table.ColumnNames definitely returns a list, where each item in the list is of type text.
I guess that's what {Text} is supposed to mean (in M a list can be expressed as a comma-separated list between curly braces).

 

[absherzad]

Thanks for the input and now that is clear
By the way for the sake of curiosity - why when creating a new parameter with suggested values from a query uses Table.ColumnNames does not show the values as a list to choose from?

 

[MarcelBeug]

You can verify the type of a list with function Type.ListItem.

The following query returns text, confirming that Table.ColumnNames returns a list with type {text}:

let
    Source = Table.ColumnNames(#table(2,{{}})),
    Custom1 = Type.ListItem(Value.Type(Source))
in
    Custom1

This query and parameter let's you choose a column value when editing the parameter:

Query ColumnNames:

let
    Source = Table.ColumnNames(#table(2,{{}}))
in
    Source

Parameter ColumnName (code resulting from creating a new parameter via the user interface, using output from query ColumnNames):

"Column2" meta [IsParameterQuery=true, ExpressionIdentifier=ColumnNames, Type="Text", IsParameterQueryRequired=true]

 

[absherzad]

Thank you for clarifying. Frankly speaking I could not figure this out Source(2,{{}}). The following code returns type conversion error:

let
    Source = Excel.CurrentWorkbook(){[Name="MasterTable"]}[Content],
    #"Column Names" = Table.ColumnNames(Source(2,{{}}))
in
    #"Column Names"

 

[MarcelBeug]

The #table(2,{{}}) part just creates an empty table with 2 columns.

You can use

#"Column Names" = Table.ColumnNames(Source)

 

[absherzad]

Yes. But it does not show a list box to select a column name. One have to type the column name instead of choosing. Please see attachment.

 

[MarcelBeug]

Sorry I won't check the attachment. You will get a dropdown list if you use option "edit parameters".

 

[absherzad]

It is interesting, I did not notice the "edit parameters" options. A week ago I wrote the code properly returning the column names, however, I was wondering why the drop-down option is not available

Thanks a lot