python - 使用 pyodbc 从 SQL Server 中提取的数据行是 "unhashable type"

Question

我目前正在根据用户输入从 MS SQL Server 2008 查询数据。但是，当我尝试使用 describe() 函数获取五位数摘要时出现错误。

import pyodbc
import numpy as np
import pandas.io.sql as sql
import pandas

print "What Part Number will you examine?"
PartN = raw_input()

conn = pyodbc.connect('my connection info')
curs = conn.cursor()
sqlr = """SELECT partmadeperhour FROM Completions WHERE  PartNumber = ?  
AND endtime > '2012-12-31 23:59:00' ORDER BY partmadeperhour"""


q = curs.execute(sqlr,[PartN]).fetchall()

df = pandas.DataFrame(q, columns =['rate'])
print df



columnnames = list(df.columns.values)
print columnnames

df['rate'].describe()

我的数据框看起来像这样

       rate
0      [0.25]
1      [0.67]
2      [0.93]
...       ...
1474   [5400.00]

我得到以下返回和错误:

[1475 rows x 1 columns]
['rate']
rate    object
dtype: object
Traceback (most recent call last):

File "newr.py", line 30, in <module>
    df['rate'].describe()

 File "C:\Python27\lib\site-packages\pandas\core\generic.py", line 4034, in describe
return describe_1d(self, percentiles)

  File "C:\Python27\lib\site-packages\pandas\core\generic.py", line 4031, in describe_1d
return describe_categorical_1d(data)

    File "C:\Python27\lib\site-packages\pandas\core\generic.py", 
line 4007, in describe_categorical_1d
objcounts = data.value_counts()

  File "C:\Python27\lib\site-packages\pandas\core\base.py", line 433, in value_counts
normalize=normalize, bins=bins, dropna=dropna)

 File "C:\Python27\lib\site-packages\pandas\core\algorithms.py", line 245, in value_counts
keys, counts = htable.value_count_object(values, mask)

 File "pandas\hashtable.pyx", line 983, in pandas.hashtable.value_count_object 
(pandas\hashtable.c:17616)

 File "pandas\hashtable.pyx", line 994, in pandas.hashtable.value_count_object 
(pandas\hashtable.c:17353)
TypeError: unhashable type: 'pyodbc.Row'

我知道我需要将数据框中的数据转换为与当前对象不同的类型，但不确定如何转换为 float 。

感谢任何帮助

Answer 1

确保您使用的是 pandas 0.12 或更高版本:

>>> import pandas
>>> pandas.__version__
'0.14.1'

使用pandas.read_sql_query直接填充数据框，传递查询字符串和 pyodbc 连接。请注意，列别名 rate 已添加到 T-SQL 查询中，因为 pandas.read_sql_query 不支持传递列名列表或字典:

...
>>> sql = "select 0.25 union select 0.67 union select 0.93 as rate" 
>>> df = pandas.read_sql_query(sql, connection)
>>> df
   rate
0  0.25
1  0.67
2  0.93
>>> df['rate'].describe()
count    3.000000
mean     0.616667
std      0.343123
min      0.250000
25%      0.460000
50%      0.670000
75%      0.800000
max      0.930000
dtype: float64

可以使用 pandas.read_sql_query 的 params 参数提供原始查询中的参数值。