KeyError:列名

Question

我像这样加载一个数据集：

df_performance = pd.read_csv('.local.csv')
df_performance.head()

csv文件中的数据已显示为表格。打印头和普通的一样。但是，当我尝试运行此代码片段时：

df_performance["Day"] = ""

df_performance.loc['Day'] = [str(x) for x in df_performance.loc["From"]]

我得到这样的错误：

KeyError                                  Traceback (most recent call last)
/opt/anaconda3/lib/python3.8/site-packages/pandas/core/indexes/base.py in get_loc(self, key, method, tolerance)
   2645             try:
-> 2646                 return self._engine.get_loc(key)
   2647             except KeyError:

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/index.pyx in pandas._libs.index.IndexEngine.get_loc()

pandas/_libs/index_class_helper.pxi in pandas._libs.index.Int64Engine._check_type()

KeyError: 'From'

During handling of the above exception, another exception occurred:

我还尝试打印列的名称，我知道'From‘是存在的。那么为什么我会得到这样的错误呢？

for col_name in df_performance:
    print(col_name)

    From           Cost   helps
0   Jan 1, 2020      3      4       

Answer 1

如果使用loc，它将按标签而不是列名选择索引。因此，如果不存在标签，则会引发错误：

df_performance.loc['Day'] = [str(x) for x in df_performance.loc["From"]]

因此似乎需要将列转换为字符串：

#by list comprehension
df_performance['Day'] = [str(x) for x in df_performance["From"]]

#by function
df_performance['Day'] = df_performance["From"].astype(str)