# What do you call a machine learning category encoder that involves counts?

At work I often have a variable encoding where you count the number of each category with respect to a key. (Which makes sense for the domain I am in) Does this process have a machine learning or statistical name?

Recently, I realized from Encoding Categorical Features that is not exactly "one-hot encoding". For example, given this data:

+----+----------+-----+
| id | category | y   |
+----+----------+-----+
| 1  | A        | 40  |
+----+----------+-----+
| 1  | B        | 40  |
+----+----------+-----+
| 1  | C        | 40  |
+----+----------+-----+
| 2  | B        | 50  |
+----+----------+-----+
| 3  | A        | 100 |
+----+----------+-----+
| 3  | A        | 100 |
+----+----------+-----+
| 3  | C        | 100 |
+----+----------+-----+


I normally get this:

+----+---+---+---+----+
| id | A | B | C | y  |
+----+---+---+---+----+
| 1  | 1 | 1 | 1 | 40 |
+----+---+---+---+----+
| 2  | 0 | 1 | 0 | 50 |
+----+---+---+---+----+
| 3  | 2 | 0 | 1 |100 |
+----+---+---+---+----+


Which makes sense because a repeated category in this particular database is a measure severity and intensity. However, one-hotting is apparently this:

+----+---+---+---+----+
| id | A | B | C | y  |
+----+---+---+---+----+
| 1  | 1 | 1 | 1 | 40 |
+----+---+---+---+----+
| 2  | 0 | 1 | 0 | 50 |
+----+---+---+---+----+
| 3  | 1 | 0 | 1 |100 |
+----+---+---+---+----+


My question is this a common procedure and if so what is its name?

• Sorry this is my first time, posting so I edited the example so the question make sense. The difference is in row 3 column A. – pierround Dec 17 '19 at 18:09

## 1 Answer

The first thing that comes to my mind is a term related to database management. If this is what you are looking for, this is generally called a pivot:

https://en.m.wikipedia.org/wiki/Pivot_table

• Thank you, I realized I was overcomplicating things a little because in BI they have pivots and unpivots and other different names for what are essentially rotation and aggregation of data. – pierround Feb 5 at 14:21