python - Pandas 蟒 : Col[C] if value is in Col[A] and Col[B]

Question

我有一个像这样的数据框:

    ColA             ColB                        ColC
"lorem ipsum"     ["lorem", "foo", "bar"]
"lorem ipsum"      NaN
NaN                ["lorem", "foo", "bar"]
NaN                 NaN

我正在尝试获取此输出:

    ColA             ColB                        ColC
"lorem ipsum"     ["lorem", "foo", "bar"]       "lorem"

我试过像这样使用理解列表:

df["C"] = [elem for elem in df["B"] if elem in df["A"] ]

但没有成功:

TypeError: unhashable 类型: 'list'如果我将 ColB 格式化为列表，并且ValueError:值的长度与索引的长度不匹配如果我使用元组

一些帮助将不胜感激，谢谢。

编辑 + 编辑 2:两列中只有一个词(或无)，我需要捕获它以将其放在 C 列中。我还忘了提及 ColA 和 ColB 可以将 NaN 作为值。

Answer 1

通过try+except 使用自定义函数并通过pipe 传递DataFrame :

df = pd.DataFrame({'A':['lorem ipsum','lorem ipsum',np.nan, np.nan],
                   'B':[["lorem", "foo", "bar"], np.nan, ["lorem", "foo", "bar"], np.nan]})
print (df)
             A                  B
0  lorem ipsum  [lorem, foo, bar]
1  lorem ipsum                NaN
2          NaN  [lorem, foo, bar]
3          NaN                NaN

def test(df):
    out = []
    for a, b in zip(df["A"], df["B"]):
        try:
            out.append(next(y for y in b if y in a))
        except Exception:
            out.append('')
    return out

df["C"] = df.pipe(test)
print (df)
             A                  B      C
0  lorem ipsum  [lorem, foo, bar]  lorem
1  lorem ipsum                NaN       
2          NaN  [lorem, foo, bar]       
3          NaN                NaN       

另一种解决方案效果不佳:

df = df.fillna("undefined")
df["C"] = [next((y for y in b if y in a), '') for a, b, in zip(df["A"],df["B"])]
print (df)


             A                  B  C
0  lorem ipsum      [d, foo, bar]   
1  lorem ipsum          undefined  u
2    undefined  [lorem, foo, bar]   
3    undefined          undefined  u