# Dealing with categorical variables in regression problems which method to use?

Usually if I have regression problem and my initial dataset contains categorical variables like :

column 1:
Math
Science
Science
English


I would convert this non-numerical variables to numerical variable such that : Math: 0, Science : 1, English : 2. However, I recently found a tutorial said that this solution is not performant because there is no favorite class among other means there is no increase between those classes and if it existe we can not quantify it.

Can anyone explain this for me because I usually worked with solution one ?