python - Pandas :如果 A 列中的行包含 "x"，则将 "y"写入 B 列中的行

Question

对于 pandas ，我正在寻找一种方法，根据 A 列中相应行的子字符串，将条件值写入 B 列中的每一行。

因此，如果 A 中的单元格包含 "BULL" , 写 "Long"至 B .或者如果单元格在 A包含 "BEAR" , 写 "Short"至 B .

期望的输出:

A                  B
"BULL APPLE X5"    "Long"
"BEAR APPLE X5"    "Short"
"BULL APPLE X5"    "Long"

B 最初是空的: df = pd.DataFrame([['BULL APPLE X5',''],['BEAR APPLE X5',''],['BULL APPLE X5','']],columns=['A','B'])

Answer 1

当您错误地创建数据框时，您的代码会出错，只需创建一个列 A然后添加 B基于 A :

import pandas as pd
df = pd.DataFrame(["BULL","BEAR","BULL"], columns=['A'])
df["B"] = ["Long" if ele  == "BULL" else "Short" for ele in df["A"]]

print(df)

    A      B
0  BULL   Long
1  BEAR  Short
2  BULL   Long

或者在创建数据框之前对数据进行逻辑处理:

import pandas as pd
data = ["BULL","BEAR","BULL"]
data2 = ["Long" if ele  == "BULL" else "Short" for ele in data]
df = pd.DataFrame(list(zip(data, data2)), columns=['A','B'])

print(df)
      A      B
 0  BULL   Long
 1  BEAR  Short
 2  BULL   Long

对于您的编辑:

df = pd.DataFrame([['BULL APPLE X5',''],['BEAR APPLE X5',''],['BULL APPLE X5','']], columns=['A','B'])

df["B"] = df["A"].map(lambda x: "Long" if "BULL" in x else "Short" if "BEAR" in x else "")

print(df)

            A      B
0  BULL APPLE X5   Long
1  BEAR APPLE X5  Short
2  BULL APPLE X5   Long

或者只是在后面添加列:

df = pd.DataFrame(['BULL APPLE X5','BEAR APPLE X5','BLL APPLE X5'], columns=['A'])

df["B"] = df["A"].map(lambda x: "Long" if "BULL" in x else "Short" if "BEAR" in x else "")

print(df)

或使用包含:

df = pd.DataFrame([['BULL APPLE X5',''],['BEAR APPLE X5',''],['BULL APPLE X5','']], columns=['A','B'])


df["B"][df['A'].str.contains("BULL")] = "Long"
df["B"][df['A'].str.contains("BEAR")] = "Short"

print(df)
0  BULL APPLE X5   Long
1  BEAR APPLE X5  Short
2  BULL APPLE X5   Long