在 Tableau 中使用 COUNT 按组计算观察值

Question

Thanks in advance for any advice you can offer! I'm building a Tableau dashboard to explore housing affordability and school quality in different neighborhoods in my area. A user will select their occupation and see a graph of neighborhoods plotted based on school quality and housing affordability. To explore housing affordability, I'm using county level assessor data with the valuation of every property matched to neighborhoods.

The goal is to display the percentage of homes in an area that are affordable given the median occupational wages for the job a user selected. Right now, I'm trying to use a calculated field with COUNT([Parcels]<[Occupation])/COUNT([Parcels]) , but I need to find a way to count the number of properties in each specific neighborhood below the cut off value.

Does anyone know of a way to count elements of a particular group in this way in Tableau?

I'm on a Mac, using Tableau Desktop, and doing the back end analysis work in R. Thank you!

Answer 1

You seem to misunderstand what the function COUNT() does. You are certainly not alone. Count() behaves in Tableau almost identically to how it does with SQL.

Count([some field]) returns the number of data rows where the value for [some field] is not null. It does not not return the number of rows where [some field] evaluates to true, or a positive number, or anything else.

If [some field] always has a non-null value, then Count([some field]) is the same as SUM([Number of Records]). If [some field] is always null, then Count([some field]) is zero. Count() is not like Excel's CountIf function.

If you want to count data rows that meet a condition, you could try COUNT(if [condition] then 1 end) Since the missing ELSE case defaults to null values, that expression will count rows where [condition] is true.

So one way to get the percentage of affordable homes is count(if [affordable] then 1 end) / count(1) assumes each Data row represents a home. Then format your field to display as a percentage. Another option is to learn to use quick table calcs

Answer 2

If you want to display the number of rows in a given visualized table you could also use SIZE()

Source, official docs: https://help.tableau.com/current/pro/desktop/en-us/functions_functions_tablecalculation.htm#size