Matplotlib条形图x轴不打印字符串值

Question

我叫大卫，我在佛罗里达的一家救护车公司工作。

我正在使用Python 2.7和matplotlib。我正试图进入我的救护车呼叫数据库，并统计每个工作日发生的呼叫次数。

然后，我将使用matplotlib创建此信息的条形图，以向医护人员显示他们每天的忙碌程度。

下面是非常有效的代码：

import pyodbc
import matplotlib.pyplot as plt
MySQLQuery = """
SELECT 
 DATEPART(WEEKDAY, IIU_tDispatch)AS [DayOfWeekOfCall]
, COUNT(DATEPART(WeekDay, IIU_tDispatch)) AS [DispatchesOnThisWeekday]
FROM AmbulanceIncidents
GROUP BY DATEPART(WEEKDAY, IIU_tDispatch)
ORDER BY DATEPART(WEEKDAY, IIU_tDispatch)
"""
cnxn = pyodbc.connect('DRIVER={SQL Server};SERVER=MyServer;DATABASE=MyDatabase;UID=MyUserID;PWD=MyPassword')
cursor = cnxn.cursor()
GraphCursor = cnxn.cursor()
cursor.execute(MySQLQuery)

#generate a graph to display the data
data = GraphCursor.fetchall()
DayOfWeekOfCall, DispatchesOnThisWeekday = zip(*data)
plt.bar(DayOfWeekOfCall, DispatchesOnThisWeekday)
plt.grid()
plt.title('Dispatches by Day of Week')
plt.xlabel('Day of Week')
plt.ylabel('Number of Dispatches')
plt.show()

上面显示的代码工作得很好。它返回一个漂亮的图表，我很高兴。我只想做一个改变。

它显示的是整数，而不是显示一周中日期的名称的X轴，例如“Sunday”。换句话说，星期天是1，星期一是2，等等

我的修正是，我改写我的SQL查询使用DeNeNeMe（）代替DATEPARTE（）。 下面显示的是我的sql代码，用于返回周的名称（而不是整数）。

SELECT 
 DATENAME(WEEKDAY, IIU_tDispatch)AS [DayOfWeekOfCall]
, COUNT(DATENAME(WeekDay, IIU_tDispatch)) AS [DispatchesOnThisWeekday]
FROM AmbulanceIncidents
GROUP BY DATENAME(WEEKDAY, IIU_tDispatch)
ORDER BY DATENAME(WEEKDAY, IIU_tDispatch)

我的python代码中的其他内容保持不变。但是这不起作用，我无法理解错误消息。

以下是错误消息：

Traceback (most recent call last):
  File "C:\Documents and Settings\kulpandm\workspace\FiscalYearEndReport\CallVolumeByDayOfWeek.py", line 59, in 

<module>
    plt.bar(DayOfWeekOfCall, DispatchesOnThisWeekday)
  File "C:\Python27\lib\site-packages\matplotlib\pyplot.py", line 2080, in bar
    ret = ax.bar(left, height, width, bottom, **kwargs)
  File "C:\Python27\lib\site-packages\matplotlib\axes.py", line 4740, in bar
    self.add_patch(r)
  File "C:\Python27\lib\site-packages\matplotlib\axes.py", line 1471, in add_patch
    self._update_patch_limits(p)
  File "C:\Python27\lib\site-packages\matplotlib\axes.py", line 1489, in _update_patch_limits
    xys = patch.get_patch_transform().transform(vertices)
  File "C:\Python27\lib\site-packages\matplotlib\patches.py", line 547, in get_patch_transform
    self._update_patch_transform()
  File "C:\Python27\lib\site-packages\matplotlib\patches.py", line 543, in _update_patch_transform
    bbox = transforms.Bbox.from_bounds(x, y, width, height)
  File "C:\Python27\lib\site-packages\matplotlib\transforms.py", line 745, in from_bounds
    return Bbox.from_extents(x0, y0, x0 + width, y0 + height)
TypeError: coercing to Unicode: need string or buffer, float found

我想不通。

综上所述，当我用x轴作为整数输出数据时，y轴显示救护车事故的数量，Matplotlib将生成一个很好的图表。但当我的数据输出是x轴时，它是一个字符串（星期日、星期一等）。那么Matplotlib将不工作。

我在Google上做了几个小时的研究，阅读了matplotlib文档。 请帮帮我。我希望使用Matplotlib作为我的报告引擎。

Answer 1

解决问题的最终完整答案： 非常感谢史蒂夫。你帮了大忙。我在大学学的是地理，不是编程，所以这对我来说很难。 这是我的最终代码。

 import pyodbc
    import matplotlib.pyplot as plt
    MySQLQuery = """
    SELECT 
      DATEPART(WEEKDAY, IIU_tDispatch)AS [IntegerOfDayOfWeek]
    , COUNT(DATENAME(WeekDay, IIU_tDispatch)) AS [DispatchesOnThisWeekday]
    , DATENAME(WEEKDAY, IIU_tDispatch)AS [DayOfWeekOfCall]
    FROM IIncidentUnitSummary
    INNER JOIN PUnit ON IIU_kUnit = PUN_Unit_PK
    WHERE PUN_UnitAgency = 'LC'
    AND IIU_tDispatch BETWEEN 'October 1, 2010' AND 'October 1, 2011'
    AND PUN_UnitID LIKE 'M__'
    GROUP BY DATEPART(WEEKDAY, IIU_tDispatch), DATENAME(WEEKDAY, IIU_tDispatch)
    ORDER BY DATEPART(WEEKDAY, IIU_tDispatch)
    """
    cnxn = pyodbc.connect("a bunch of stuff I don't want to share")
    cursor = cnxn.cursor()
    GraphCursor = cnxn.cursor()
    cursor.execute(MySQLQuery)

    results = cursor.fetchall()
    IntegerDayOfWeek, DispatchesOnThisWeekday, DayOfWeekOfCall = zip(*results)
    tickpositions = [int(r[0]) for r in results]
    numincidents = [int(r[1]) for r in results]
    ticklabels = [r[2] for r in results]
    plt.bar(tickpositions, numincidents)
    plt.xticks(tickpositions, ticklabels)
    #plt.bar(DayOfWeekOfCall, DispatchesOnThisWeekday)
    plt.grid()
    plt.title('Dispatches by Day of Week')
    plt.xlabel('Day of Week')
    plt.ylabel('Number of Dispatches')
    plt.show()

    cursor.close()
    cnxn.close()

我真的不明白“results=cursor.fetchall（）”和下面四行涉及创建数组的代码之间的关系。我很高兴你这样做，因为我看着它，它仍然没有下沉。 非常感谢你。这帮了大忙。 大卫