如何在 pandas 中制作分类组列

Question

Given a column of “food” (apple, banana, carrot, donuts, egg,...), I want to make the “category” column that contains values which correspond to each item in “food” column.

Ex. given the information below

import pandas as pd

fruit =['apple', 'banana', 'orange']
veg =['carrot', 'onion']
meat=['chicken', 'pork', 'beef']

food = fruit + veg + meat

df = pd.DataFrame(food, columns=['food'])
df

When I write the code like this:

df[df['food']=='apple']['category']='fruit'
df[df['food']=='carrot']['category']='vegetable'

However, a SettingWithCopyWarning occurs when I write down in this way.

What would be the best way to set this value?

Answer 1

You probably got a SettingWithCopy warning from pandas. You can resolve that in a few different ways:

# Use loc
df['category'] = None # Initialize an empty column
df.loc[df['food']=='apple',  'category'] = 'fruit'
df.loc[df['food']=='carrot', 'category'] = 'vegetable'

# Use map
df['category'] = df['food'].map({
    'apple': 'fruit',
    'carrot': 'vegetable'
})