Question

我有以下带有某些缺失值的DataFrame。我想使用ffill()来填充var1和var2分组的date和building中的缺失值。我可以一次为一个变量执行此操作，但是当我尝试同时为两个变量执行操作时，它将崩溃。如何在不修改但保留var3或var4的情况下同时对两个变量执行此操作？

df = pd.DataFrame({
    'date': ['2019-01-01','2019-01-01','2019-01-01','2019-01-01','2019-02-01','2019-02-01','2019-02-01','2019-02-01'],
    'building': ['a', 'a', 'b', 'b', 'a', 'a', 'b', 'b'],
    'var1': [1.5, np.nan, 2.1, 2.2, 1.2, 1.3, 2.4, np.nan],
    'var2': [100, 110, 105, np.nan, 102, np.nan, 103, 107],
    'var3': [10, 11, np.nan, np.nan, np.nan, np.nan, np.nan, np.nan],
    'var4': [1, 2, 3, 4, 5, 6, 7, 8]
})
df  
    date  building  var1    var2    var3    var4
0   2019-01-01  a   1.5    100.0    10.0    1
1   2019-01-01  a   NaN    110.0    11.0    2
2   2019-01-01  b   2.1    105.0    NaN     3
3   2019-01-01  b   2.2    NaN      NaN     4
4   2019-02-01  a   1.2    102.0    NaN     5
5   2019-02-01  a   1.3    NaN      NaN     6
6   2019-02-01  b   2.4    103.0    NaN     7
7   2019-02-01  b   NaN    107.0    NaN     8

# This works
df['var1'] = df.groupby(['date', 'building'])['var1'].ffill()
df['var2'] = df.groupby(['date', 'building'])['var2'].ffill()
df
        date  building  var1    var2    var3    var4
0   2019-01-01  a        1.5    100.0   10.0    1
1   2019-01-01  a        1.5    110.0   11.0    2
2   2019-01-01  b        2.1    105.0   NaN     3
3   2019-01-01  b        2.2    105.0   NaN     4
4   2019-02-01  a        1.2    102.0   NaN     5
5   2019-02-01  a        1.3    102.0   NaN     6
6   2019-02-01  b        2.4    103.0   NaN     7
7   2019-02-01  b        2.4    107.0   NaN     8

# This doesn't work
df[['var1', 'var2']] = df.groupby(['date', 'building'])[['var1', 'var2']].ffill()
ValueError: Columns must be same length as key

Answer 1

反复进行：

gb = df.groupby(['date', 'building'])
for g in ["var1", "var2"]:
    df[g] = gb[g].ffill()

         date building  var1   var2  var3  var4
0  2019-01-01        a   1.5  100.0  10.0     1
1  2019-01-01        a   1.5  110.0  11.0     2
2  2019-01-01        b   2.1  105.0   NaN     3
3  2019-01-01        b   2.2  105.0   NaN     4
4  2019-02-01        a   1.2  102.0   NaN     5
5  2019-02-01        a   1.3  102.0   NaN     6
6  2019-02-01        b   2.4  103.0   NaN     7
7  2019-02-01        b   2.4  107.0   NaN     8

Answer 2

@Gaurav Bansal在数据框中按分组进行拟合时，您只是缺少了几列。

df[['date', 'building','var1', 'var2']] = df.groupby(['date', 'building'])[['var1', 'var2']].ffill()

Group by将返回四列数据框，它们是'date'，building'，'var1'和'var2'，或者您可以只提供一个数据框来存储操作的数据框。

>

因此您需要将其存储到四列df中，以与返回的键值完美匹配。

Answer 3

我认为您需要在fillna之前添加groupby。

df[["var1", "var2"]] = df[["var1", "var2"]].fillna(df.groupby(['date', 'building'])[["var1", "var2"]].ffill())

    date    building    var1    var2    var3    var4
0   2019-01-01  a   1.5 100.0   10.0    1
1   2019-01-01  a   1.5 110.0   11.0    2
2   2019-01-01  b   2.1 105.0   NaN 3
3   2019-01-01  b   2.2 105.0   NaN 4
4   2019-02-01  a   1.2 102.0   NaN 5
5   2019-02-01  a   1.3 102.0   NaN 6
6   2019-02-01  b   2.4 103.0   NaN 7
7   2019-02-01  b   2.4 107.0   NaN 8

python-熊猫：多列填充

3 个答案: