[pandas] SettingWithCopyWarning: A value is trying to be set on a copy of a slice from a DataFrame

轉載自https://blog.csdn.net/blackyuanc/article/details/77892784

問題場景：

      在讀取CSV文件后，在新增一個特征列並根據已有特征修改新增列的值，結果在修改的過程中碰到SettingWithCopyWarning警告。

報錯的做法：

import pandas as pd
import numpy as np

aa = np.array([1,0,1,0])
bb = pd.DataFrame(aa.T, columns=['one'])

bb['two'] = 0

for i in range(bb.shape[0]):
        bb['two'][i] = 1

print(bb)

正確的做法：

# -*- coding: utf-8 -*-
import pandas as pd
import numpy as np

aa = np.array([1,0,1,0])
bb = pd.DataFrame(aa.T, columns=['one'])

# 建立
two = np.zeros(bb.shape[0])

# 修改
for i in range(bb.shape[0]):
    two[i] = random.random()

# 插入
bb.insert(0,'two',two)

print(bb)