如何根据一列中的匹配值连接两个数据框？

Question

I start with two dataframes:

              Breakfast        Lunch
1  Monday     Cereal           Sandwich
2  Wednesday  Eggs             Salad

              Dinner           Snack
1  Monday     Ham              Chips
2  Tuesday    Pasta            Nuts
3  Wednesday  Chicken          Apple

How can I join these two dataframes comparing weekdays in to something like:

              Breakfast        Lunch        Dinner           Snack
1  Monday     Cereal           Sandwich     Ham              Chips
2  Tuesday                                  Pasta            Nuts
3  Wednesday  Eggs             Salad        Chicken          Apple

Answer 1

You can join (to take advantage of the fact that you're merging on index); then groupby index level 1 (which are days of the week) and use first (which by default drops NaN values)

out = df1.join(df2, how='outer').groupby(level=1).first().replace({None:''})

Output:

          Breakfast     Lunch   Dinner  Snack
Monday       Cereal  Sandwich      Ham  Chips
Tuesday                          Pasta   Nuts
Wednesday      Eggs     Salad  Chicken  Apple