我认为可以通过将numpy.random.permutation应用于index来使reindex加倍，但是两个DataFrame必须具有相同的长度和相同的唯一索引值：

df1 = pd.DataFrame({'a':range(5)})
print (df1)
   a
0  0
1  1
2  2
3  3
4  4

df2 = pd.DataFrame({'a':range(5)})
print (df2)
   a
0  0
1  1
2  2
3  3
4  4

idx = np.random.permutation(df1.index)
print (df1.reindex(idx))
   a
2  2
4  4
1  1
3  3
0  0

print (df2.reindex(idx))
   a
2  2
4  4
1  1
3  3
0  0

reindex_axis的替代方案：

print (df1.reindex_axis(idx, axis=0))
print (df2.reindex_axis(idx, axis=0))

x1, x2, y1, y2 = train_test_split(x, y, shuffle = True)
x3 = pd.concat([x1, x2])
y3 = pd.concat([y1, y2])