python - 将 Pandas 数据框中的一行复制到另一行的多行中

Question

我有 2 个具有相同列的 Pandas 数据框(df1 和 df2)，我试图将 1 行从 df1 复制到 df2 的多行。 df2是一个多索引数据框，第一个索引对应df1的索引值，第二个索引为整数值。

它们是这样定义的:

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'])

它们长什么样子:

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

下面是我如何设法将数据从 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 ，所以添加 [1] 来选择第二个:

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