Categorize objects by attribute to display count

Question

I am using the Layer Properties to categorize a large dataset by two attributes:

• manufacturer
• material

"Manufacturer" + ' - ' + "Material Type"

It's returning a long list of combinations as expected. However, I would also like to see the total count against each category in the Layer Properties before I execute, as I would like to either remove the very low count categories, or at least sort them largest to smallest. Yes, I can add show feature count in the layer panel but I want to see the count before then.

Answer 1

Go to "Layer properties — Simbology" and apply the syntax you describe in your question in "Categorized" mode. Then, switch from "Categorized" to "Rule based" (your same categories should appear but now expressed as logical expressions). There you will find a sigma button; click on it and the count for each category will appear.

Answer 2

Is it possible to define a constant number for what's a "small" category? If you have a number for the minimum size of a category then, you can apply a filter to your first expression, something like this:

if(
    count(
        1,
        group_by:=array("Manufacturer", "Material Type")
    ) >= 10, -- set here the minimum size of the category
    "Manufacturer" + ' - ' + "Material Type",
    NULL
)

And then, remove the NULL category that contains all the features that belong to a category with less than the desired minimum size.