How can I create a histogram using the superstore data, showing the distribution of unique Product Name per Order ID?

@Edwin Choo​ 

I guess you want to count how many orders have 1 product, 2 products, etc.

If this is the case, you can use:

Number of Products Per Order

{FIXED [Order ID]:COUNTD([Product Name])}

Then you can convert to Dimension:

Finally, you can add the distinct count of order ID:

This is a similar case of the first one in https://www.tableau.com/blog/LOD-expressions

Finally, if you want your dimension filters to affect the FIXED calc, then you would need to add them to the context. So, if you have a pill in the filter shelf, then right click on the pill in the filter shelf and add to context. This way, the filter will be calculated before the fixed calc:

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Regards,

Diego Martinez

Tableau Visionary and Forums Ambassador