QST: 
---

I would like to concatenate two incomplete data frame with the same data (in theory) regarding a similar index. I tried with pd.concat but I don't managed to get what I need.

Here is a simple example of what I would like to do :

```python
df1 = pd.DataFrame(
    {
        "A": ["A0", "A1", "A2", "A3"],
        "B": ["B0", "B1", "B2", "B4"],
        "C": ["C0", "C1", "C2", "B5"],
        "D": [np.nan,np.nan,np.nan,np.nan,]
    },
    index=[0, 1, 2, 3],)

df2 = pd.DataFrame(
    {
        "A": ["A0", "A1", "A5", "A6"],
        "B": ["B0", "B1", "B5", "B6"],
        "C": [np.nan,np.nan,np.nan,np.nan,],
        "D": ["D0", "D1", "D5", "D6"],
    },
    index=[0, 1, 5, 6]
)

res_expected = pd.DataFrame(
    {
        "A": ["A0",  "A1",  "A2",  "A3", "A5", "A6"],
        "B": ["B0",  "B1",  "B2",  "B3",  "B5", "B6"],
        "C": ["C0",  "C1",  "C2",  "B5",np.nan,np.nan,],
        "D": ["D0",  "D1",  np.nan,np.nan,"D5", "D6"],
    },
    index=[0, 1, 2, 3, 5, 6]
)
```

Does someone have an idea ?

Thanks !