如何匹配两个 DataFrame 中的特定值并在 Python Pandas 中添加额外的列？ [复制]

Question

如何使用 FOR LOOP 将 df_students 中的颜色与 df_colors 中的颜色进行匹配，然后在 df_students 中为每个学生填写对应的fruit和对应的fruit_id？

import pandas as pd
df_colors = pd.DataFrame({'fruit_id':[101, 102, 103, 104, 105, 106, 107, 108, 109],
                       'fruit':['apple','banana','dragonfruit','kiwi','plum','lime', 'blackberry', 'blueberry', 'guava'],
                       'color':['red', 'yellow', 'magenta', 'brown', 'purple', 'green', 'black', 'blue', 'pink']})

df_students = pd.DataFrame({'student':['Jamie', 'Tao', 'Ingrid', 'Will', 'Boris','Xavier','Nancy', 'Judith', 'Lamar', 'Francis', 'Shawna', 'Carlos', 'Morgan'],
                        'color': ['black', 'red', 'magenta', 'yellow','black', 'magenta', 'brown', 'purple', 'magenta', 'green', 'blue', 'pink', 'pink']})


df_students['fruit'] = ''
df_students['fruit_id'] = ''
for eachstudent in df_students['color']:
    for acolor in df_colors['color']:
        if eachstudent == acolor:
            df_students['fruit'] = df_colors['fruit']
            df_students['fruit_id'] = df_colors['fruit_id']
df_students

这个输出不正确！

Answer 1

import pandas as pd

df_colors = pd.DataFrame({'fruit_id':[101, 102, 103, 104, 105, 106, 107, 108, 109],
                   'fruit':['apple','banana','dragonfruit','kiwi','plum','lime', 'blackberry', 'blueberry', 'guava'],
                   'color':['red', 'yellow', 'magenta', 'brown', 'purple', 'green', 'black', 'blue', 'pink']})

df_students = pd.DataFrame({'student':['Jamie', 'Tao', 'Ingrid', 'Will', 'Boris','Xavier','Nancy', 'Judith', 'Lamar', 'Francis', 'Shawna', 'Carlos', 'Morgan'],
                    'color': ['black', 'red', 'magenta', 'yellow','black', 'magenta', 'brown', 'purple', 'magenta', 'green', 'blue', 'pink', 'pink']})
df_students['fruit'] = ''
df_students['fruit_id'] = ''

for acolor1 in df_colors['color']: 
    df_students.loc[df_students['color']==acolor1,'fruit']= list(df_colors.loc[df_colors['color']==acolor1,'fruit'])[0]
    df_students.loc[df_students['color']==acolor1, 'fruit_id'] = list(df_colors.loc[df_colors['color']==acolor1, 'fruit_id'])[0]
print (df_students)

Answer 2

这个怎么样：

for num1,eachstudent in enumerate(df_students['color']):
    for num2,acolor in enumerate(df_colors['color']):
        if eachstudent == acolor:
            df_students['fruit'].values[num1] = df_colors['fruit'].values[num2]
            df_students['fruit_id'].values[num1] = df_colors['fruit_id'].values[num2]

Answer 3

你只是想执行一个合并，你不需要'for循环'。

请看Pandas Merging 101

您正在寻找的解决方案：

df_students.merge(df_colors, on='color', how='left')


    student color   fruit_id    fruit
0   Jamie   black   107         blackberry
1   Tao     red     101         apple
2   Ingrid  magenta 103         dragonfruit
3   Will    yellow  102         banana
4   Boris   black   107         blackberry
5   Xavier  magenta 103         dragonfruit
6   Nancy   brown   104         kiwi
7   Judith  purple  105         plum
8   Lamar   magenta 103         dragonfruit
9   Francis green   106         lime
10  Shawna  blue    108         blueberry
11  Carlos  pink    109         guava
12  Morgan  pink    109         guava

就像我说的，如果您想在两个数据框中的 color 列上进行匹配，那么您给出的预期输出是不正确的。