Here is a free Microsoft Power BI DAX CONCATENATEX Function Training Reference Guide by Dynamics Edge.
For more info:
Ref: CONCATENATEX function concatenates the result of an expression evaluated for each row in a table in Microsoft Power BI DAX. It is often used to iterate over a column in Power Pivot / DAX. Sometimes, FILTERS() and CONCATENATEX() , where FILTERS() returns a table of the values applied as filters to a column, are used together. This function may sometimes also be associated with Microsoft Excel 2016 as well.
Syntax of CONCATENATEX function (for PowerPivot Training and Power BI Dax Training)
It is called with this signature. CONCATENATEX(required table, required expression, optional delimiter)
|Parameter||What it means|
|table||The table means the one containing the pertinent rows that the expression will be evaluated for in DAX.|
|expression||Expression means the actual expression to be evaluated andf applied to each row of the table described above.|
|delimiter (this is optional)||The delimiter is optional, and a delimiter here means a separator to optionally use during concatenation such as a comma , a pipe | or your choice of delimiter.|
The Return Value of CONCATENATEX is a text string in Power BI DAX.
The CONCATENATEX function's very first argument is accepted as a table or alternatively, an expression that returns a table in the end. CONCATENATEX has a second argument which is a column that contains the values you actually desire to concatenate, or also an expression that returns a value as described.
Here is an Example
Demo Employees table
CONCATENATEX(Employees, [FirstName] & “ “ & [LastName], “,”)
The above example returns "Mike Brewer, Alan Blythe" assuming the above.