Question

我有2个相同列的pandas数据帧（df1和df2），我试图将df1中的1行复制到多行df2中。 df2是一个多索引数据帧，第一个索引对应于df1的索引值，第二个索引是整数值。

以下是它们的定义方式：

df1 = pd.DataFrame(index=['one', 'two', 'three'], columns=['c1', 'c2', 'c3', 'c4'], data=np.random.random((3, 4)))

index = pd.MultiIndex.from_arrays([['one', 'one', 'two', 'two', 'two', 'three'], [0, 1, 0, 1, 2, 0]])
df2 = pd.DataFrame(index=index, columns=['c1', 'c2', 'c3', 'c4'])

他们的样子：

In : df1
Out: 
             c1        c2        c3        c4
one    0.158366  0.843546  0.810493  0.925164
two    0.880147  0.464835  0.416196  0.389786
three  0.138132  0.061891  0.320366  0.727997


In : df2
Out: 
          c1   c2   c3   c4
one   0  NaN  NaN  NaN  NaN
      1  NaN  NaN  NaN  NaN
two   0  NaN  NaN  NaN  NaN
      1  NaN  NaN  NaN  NaN
      2  NaN  NaN  NaN  NaN
three 0  NaN  NaN  NaN  NaN

现在我可以设法将数据从df1复制到df2：

for index, data in df1.iterrows():
    num = len(df2.loc[index])
    for i in range(num):
        df2.loc[(index, i)] = df1.loc[index]

结果：

In : df2
Out: 
                 c1         c2        c3        c4
one   0  0.158366   0.843546  0.810493  0.925164
      1  0.158366   0.843546  0.810493  0.925164
two   0  0.880147   0.464835  0.416196  0.389786
      1  0.880147   0.464835  0.416196  0.389786
      2  0.880147   0.464835  0.416196  0.389786
three 0  0.138132  0.0618906  0.320366  0.727997

知道如何更有效地做到这一点吗？

Answer 1

您可以使用DataFrame.align，在元组中返回DataFrames，因此请为第二个添加[1]：

np.random.seed(23)
df1 = pd.DataFrame(index=['one', 'two', 'three'], columns=['c1', 'c2', 'c3', 'c4'], data=np.random.random((3, 4)))

index = pd.MultiIndex.from_arrays([['one', 'one', 'two', 'two', 'two', 'three'], [0, 1, 0, 1, 2, 0]])
df2 = pd.DataFrame(index=index, columns=['c1', 'c2', 'c3', 'c4'])

print (df1)
             c1        c2        c3        c4
one    0.517298  0.946963  0.765460  0.282396
two    0.221045  0.686222  0.167139  0.392442
three  0.618052  0.411930  0.002465  0.884032


df3 = df2.align(df1, level=0)[1]
print (df3)
               c1        c2        c3        c4
one   0  0.517298  0.946963  0.765460  0.282396
      1  0.517298  0.946963  0.765460  0.282396
two   0  0.221045  0.686222  0.167139  0.392442
      1  0.221045  0.686222  0.167139  0.392442
      2  0.221045  0.686222  0.167139  0.392442
three 0  0.618052  0.411930  0.002465  0.884032

将1行从熊猫数据帧复制到另一行的多行

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