如何为pandas数据框中的多个非现有列分配值？

Question

所以我想要做的是将列添加到数据帧并用单个值填充它们(分别为所有行).

import pandas as pd
import numpy as np

df = pd.DataFrame(np.array([[1,2],[3,4]]), columns = ["A","B"])
arr = np.array([7,8])

# this is what I would like to do
df[["C","D"]] = arr

# and this is what I want to achieve
#    A  B  C  D
# 0  1  2  7  8
# 1  3  4  7  8
# but it yields an "KeyError" sadly
# KeyError: "['C' 'D'] not in index"

如果我只是一次添加一个列,我确实知道了assign-functions以及如何解决这个问题.我只是想知道是否有一个干净而简单的方法来处理多个新列,因为我无法找到它.

Answer 1

对我来说工作:

df[["C","D"]] = pd.DataFrame([arr], index=df.index)

或者join:

df = df.join(pd.DataFrame([arr], columns=['C','D'], index=df.index))

或者assign:

df = df.assign(**pd.Series(arr, index=['C','D']))

print (df)
   A  B  C  D
0  1  2  7  8
1  3  4  7  8