pandas sort_values() 得到了一个意外的关键字参数“by”
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sort_values() got an unexpected keyword argument 'by'
提问by sakimarquis
for i in str_list: #str_list is a set contain some strings
df.loc[i].sort_values(by = 'XXX')
**TypeError**: sort_values() got an unexpected keyword argument 'by' ".
>>> type(df.loc[i])
>>> pandas.core.frame.DataFrame
But it works outside the for loop!
但它在 for 循环之外工作！
df.loc['string'].sort_values(by = 'XXX')
>>> type(df.loc['string'])
>>> pandas.core.frame.DataFrame
I'm confused.
我糊涂了。
回答by kosnik
This is because the result of the locoperator is a pandas.Seriesobject in your case. The sort_valuesin this case doesn't have a keyword argument bybecause it can only sort the series values. Have a look at the difference in the signature when you call sort valuesin a pandas.DataFrame
这是因为在您的情况下，loc运算符的结果是一个pandas.Series对象。在sort_values这种情况下没有一个关键字参数by，因为它只能排序的序列值。有一个在签名中的差异，当你调用sort values一个pandas.DataFrame
https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.sort_values.html
https://pandas.pydata.org/pandas-docs/stable/generated/pandas.DataFrame.sort_values.html
and when you call sort_valuesin a pandas.Series
当你打电话sort_values给pandas.Series
http://pandas.pydata.org/pandas-docs/version/0.22/generated/pandas.Series.sort_values.html
http://pandas.pydata.org/pandas-docs/version/0.22/generated/pandas.Series.sort_values.html
回答by Carl Kristensen
To add to the answer, why is it returning a series in one case and a data frame in another?
为了补充答案，为什么它在一种情况下返回一个系列而在另一种情况下返回一个数据框？
.loc function is returning a Series in the first case
.loc 函数在第一种情况下返回一个系列
for i in str_list: #str_list is a set contain some strings
df.loc[i].sort_values(by = 'XXX')
for i in str_list: #str_list 是一个包含一些字符串的集合
df.loc[ i].sort_values(by = 'XXX')
because the argument iappears only once in the DataFrame.
因为参数i在 DataFrame 中只出现一次。
in the second case, the 'string' is duplicated and therefore will return a DataFrame.
在第二种情况下，“字符串”被复制，因此将返回一个数据帧。
df.loc['string'].sort_values(by = 'XXX')
df.loc['string'].sort_values(by = 'XXX')
If the 'string' argument is not duplicated then note that there are also some differences if the argument in .loc is on a list. for example.
如果 'string' 参数没有重复，那么请注意，如果 .loc 中的参数在列表中，也会存在一些差异。例如。
df.loc['string'] -> returns a Series
df.loc['string'] -> 返回一个系列
df.loc[['string']] -> returns a DataFrame
df.loc[['string']] -> 返回一个 DataFrame
Maybe in the second case you are giving ['string'] as the argument instead of 'string' ?
也许在第二种情况下，您将 ['string'] 作为参数而不是 'string' ？
Hope this helps.
希望这可以帮助。
