Python Pandas - Changing some column types to categories

You can use the pandas.DataFrame.apply method along with a lambda expression to solve this. In your example you could use

df[['parks', 'playgrounds', 'sports']].apply(lambda x: x.astype('category'))

I don't know of a way to execute this inplace, so typically I'll end up with something like this:

df[df.select_dtypes(['object']).columns] = df.select_dtypes(['object']).apply(lambda x: x.astype('category'))

Obviously you can replace .select_dtypes with explicit column names if you don't want to select all of a certain datatype (although in your example it seems like you wanted all object types).

Sometimes, you just have to use a for-loop:

for col in ['parks', 'playgrounds', 'sports', 'roading']:
    public[col] = public[col].astype('category')