pandas 熊猫分类错误：“无法在具有新类别的分类上设置项目，请先设置类别”
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pandas Categorical error: "Cannot setitem on a Categorical with a new category, set the categories first"
提问by Gabriela M
I have the following df data frame in pandas:
我在Pandas中有以下 df 数据框：
weekday venta_total_cy
0 Viernes 5.430211e+09
1 Lunes 3.425554e+09
2 Sabado 6.833202e+09
3 Domingo 6.566466e+09
4 Jueves 2.748710e+09
5 Martes 3.328418e+09
6 Miercoles 3.136277e+09
What I want to do is to order the data frame by the following days' order:
我想要做的是按以下几天的顺序对数据框进行排序：
weekday
Lunes
Martes
Miercoles
Jueves
Viernes
Sabado
Domingo
To do so, I used the following code:
为此，我使用了以下代码：
df['weekday'] = pd.Categorical(df[['weekday']], categories=["Lunes", "Martes", "Miercoles", "Jueves", "Viernes", "Sabado", "Domingo"])
When I run the code, I get this error:
当我运行代码时，我收到此错误：
ValueError: Cannot setitem on a Categorical with a new category, set the categories first
I have not found enough documentation to resolve this. Can you help me? Thanks!
我还没有找到足够的文档来解决这个问题。你能帮助我吗？谢谢！
采纳答案by cs95
df[['weekday']]returns a dataframe, which is incorrect. Convert the seriescolumn to categorical instead. Also, use the ordered=Trueargument to establish order in your categorical column.
df[['weekday']]返回一个数据帧，这是不正确的。将系列列转换为分类列。此外，使用ordered=True参数在您的分类列中建立顺序。
categories = np.array(
['Lunes', 'Martes', 'Miercoles', 'Jueves', 'Viernes', 'Sabado', 'Domingo']
)
df.weekday = pd.Categorical(df.weekday, categories=categories, ordered=True)
df.sort_values(by='weekday')
weekday venta_total_cy
1 Lunes 3.425554e+09
5 Martes 3.328418e+09
6 Miercoles 3.136277e+09
4 Jueves 2.748710e+09
0 Viernes 5.430211e+09
2 Sabado 6.833202e+09
3 Domingo 6.566466e+09
