How to Calculate Select Field Option Percentages in Notion

Reader's Question

I'd like to ask — when I use Rollup to generate some statistics for my book Database, I noticed that the "count per group" calculation option only appears when the field is a Status type. It doesn't work with Select fields.

But here's the problem: some of my book statuses are "Paused" and "Dropped," and strictly speaking, I don't want to categorize them into the 3 fixed Status states (To-do, In progress, Complete).

Is there any other way to make Rollup perform a "count per group" calculation on different options under a Select field?

My Answer

First of all, the prerequisite for the "count per group" option to appear is that there must be groups. Since each option in a Select field is independent and ungrouped, this option naturally won't appear.

Status, on the other hand, is inherently a collection of three meta-states. For a detailed explanation of the Status Property, you can refer to section 2.7 of the course.

So the best solution is to skip Rollup altogether and use the more flexible and powerful Formula to solve this problem.

lets(
    all,prop("读书").map(current.prop("名称")).length(),
    done,prop("读书").filter(current.prop("单选")=="已读完").length(),
    ((done/all)*100).round()+"%"
)

Here's a breakdown of the Formula above:

1. Define variable all: 读书.map(current.名称).length() counts the total number of entries in the "Reading" Database
2. Define variable done: 读书.filter(current.单选=="已读完").length() filters and counts entries where the Select Property equals "Finished Reading"
3. Calculate percentage: ((done/all)*100).round()+"%" divides the number of finished entries by the total, multiplies by 100, rounds the result, and appends a percent sign

Once you master this Formula, you can calculate the percentage for any Select option.