pandas sort_values无法正确对数字进行排序 [英] Pandas sort_values does not sort numbers correctly

问题描述

我是熊猫的新手，正在编程环境中使用表格数据.我已经按特定的列对数据框进行了排序，但是熊猫吐出来的答案并不完全正确.

这是我使用的代码:

  league_dataframe.sort_values('overall_league_position') 

排序方法在总体联赛排名"列中产生值的结果未按升序或顺序进行排序，这是该方法的默认设置.

我做错了什么?感谢您的耐心等待！

解决方案

无论出于何种原因，您似乎都在使用一列字符串，并且 sort_values 返回的是按字母顺序排序的结果.

这是一个例子.

  df = pd.DataFrame({"Col":['1'，'2'，'3'，'10'，'20'，'19']})df上校0 11 22 33 104 205 19df.sort_values('Col')上校0 13 105 191 24 202 3 

补救方法是使用 .astype 或 pd.to_numeric 将其转换为数字.

  df.Col = df.Col.astype(float) 

或者，

  df.Col = pd.to_numeric(df.Col，errors ='coerce') 

  df.sort_values('Col')上校0 11 22 33 105 194 20 

b/w astype 和 pd.to_numeric 的唯一区别是，后者在处理非数字字符串时更健壮(它们被强制为NaN )，并且如果不需要强制浮点(在这种情况下就是如此)，则会尝试保留整数.

I'm new to pandas and working with tabular data in a programming environment. I have sorted a dataframe by a specific column but the answer that panda spits out is not exactly correct.

Here is the code I have used:

league_dataframe.sort_values('overall_league_position')

The result that the sort method yields values in column 'overall league position' are not sorted in ascending or order which is the default for the method.

What am I doing wrong? Thanks for your patience!

解决方案

For whatever reason, you seem to be working with a column of strings, and sort_values is returning you a lexsorted result.

Here's an example.

df = pd.DataFrame({"Col": ['1', '2', '3', '10', '20', '19']})
df

  Col
0   1
1   2
2   3
3  10
4  20
5  19

df.sort_values('Col')

  Col
0   1
3  10
5  19
1   2
4  20
2   3

The remedy is to convert it to numeric, either using .astype or pd.to_numeric.

df.Col = df.Col.astype(float)

Or,

df.Col = pd.to_numeric(df.Col, errors='coerce')

df.sort_values('Col')

   Col
0    1
1    2
2    3
3   10
5   19
4   20

The only difference b/w astype and pd.to_numeric is that the latter is more robust at handling non-numeric strings (they're coerced to NaN), and will attempt to preserve integers if a coercion to float is not necessary (as is seen in this case).

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