Sharing: How to create test data using DAX!

[stevedep]

Hi,

In this article, I will show how to generate sample data and how to add this to your data model. 

The result is a sales table and related dimensions:

This is the code to generate the sales table:

Sales = 
VAR _tbl =
    SELECTCOLUMNS (
        CROSSJOIN ( ROW ( "test", DATE ( 2020, 10, 3 ) ), GENERATESERIES ( 1, 60, 1 ) ),
        "StartDate", [test],
        "Increment", [Value]
    )
VAR _dates =
    ADDCOLUMNS ( _tbl, "NewDate", [StartDate] + [Increment] )
RETURN
    GENERATE (
        SELECTCOLUMNS (
            { "Vendor 1", "Vendor 2", "Vendor 3", "Vendor 4", "Vendor 5" },
            "Vendor", [Value]
        ),
        SELECTCOLUMNS (
            ADDCOLUMNS (
                CROSSJOIN ( _dates, GENERATESERIES ( 1, 10, 1 ) ),
                "open_time",
                    [NewDate]
                        + NORM.INV ( RAND (), 0.5 + ( [Increment] / 100 ), 0.08 ),
                "PRODUCT",
                    CONVERT ( UNICHAR ( RANDBETWEEN ( 65, 90 ) ), STRING )
                        & CONVERT ( UNICHAR ( RANDBETWEEN ( 65, 90 ) ), STRING )
                        & CONVERT ( UNICHAR ( RANDBETWEEN ( 65, 90 ) ), STRING ),
                "sales_amount", NORM.INV ( RAND (), [Value], [Value] / 10 )
            ),
            "sales_date_time", [open_time],
            "PRODUCT", [PRODUCT],
            "sales_amount", [sales_amount]
        )
    )

You can add the above code by navigating to the ribbon in Power BI, select 'Modelling' to then select 'New Table'. Paste the above code in the editor. 

Explanation

In the next part, I will break down the working of the code. 

First, we generate a series of dates:

We started with a default date and added an incremental column, that column sets the number of days that we will add to the default data. 

Next is adding vendors:

     SELECTCOLUMNS (
            { "Vendor 1", "Vendor 2", "Vendor 3", "Vendor 4", "Vendor 5" },
            "Vendor", [Value]

For each vendor, all the dates (generated above) are added and a timestamp is added:

  SELECTCOLUMNS (
            ADDCOLUMNS (
                CROSSJOIN ( _dates, GENERATESERIES ( 1, 10, 1 ) ),
                "open_time",
                    [NewDate]
                        + NORM.INV ( RAND (), 0.5 + ( [Increment] / 100 ), 0.08 ),

A product is added by randomly selected characters from the UNICHAR array:

 "PRODUCT",
                    CONVERT ( UNICHAR ( RANDBETWEEN ( 65, 90 ) ), STRING )
                        & CONVERT ( UNICHAR ( RANDBETWEEN ( 65, 90 ) ), STRING )
                        & CONVERT ( UNICHAR ( RANDBETWEEN ( 65, 90 ) ), STRING ),

A sales amount is added:

      "sales_amount", NORM.INV ( RAND (), [Value], [Value] / 10 )

Finally, the required columns are added:

            "sales_date_time", [open_time],
            "PRODUCT", [PRODUCT],
            "sales_amount", [sales_amount]
        )

With the above steps, we have created the fact table. With that table in place we can add the dimension tables by simply adding a table with DAX like below:

dimProducts = VALUES(Sales[PRODUCT])

As a final step, we add the relationships in the data model. That is hopefully on familiar grounds. 

You can have fun with generating data and creating art from it as well 🙂 , see below:

The above image is from a response that I wrote when helping out somebody with a DAX challenge. 

Hope that you find it useful. An example is attached.

Kind regards, 

Steve.