让我们看下面的人为示例，我创建 aDataFrame然后DatetimeIndex使用具有重复条目的列创建 a。然后我将其DataFrame放入 aPanel中，然后尝试在主轴上进行迭代。
import pandas as pd
import datetime as dt
a = [1371215933513120, 1371215933513121, 1371215933513122, 1371215933513122]
b = [1,2,3,4]
df = pd.DataFrame({'a':a, 'b':b, 'c':[dt.datetime.fromtimestamp(t/1000000.) for t in a]})
df.index=pd.DatetimeIndex(df['c'])
d = OrderedDict()
d['x'] = df
p = pd.Panel(d)
for y in p.major_axis:
print y
print p.major_xs(y)
这导致以下输出：
2013-06-14 15:18:53.513120
x
a 1371215933513120
b 1
c 2013-06-14 15:18:53.513120
2013-06-14 15:18:53.513121
x
a 1371215933513121
b 2
c 2013-06-14 15:18:53.513121
2013-06-14 15:18:53.513122
其次是一个相当神秘的（对我来说）错误：
---------------------------------------------------------------------------
ValueError Traceback (most recent call last)
<ipython-input-35-045aaae5a074> in <module>()
13 for y in p.major_axis:
14 print y
---> 15 print p.major_xs(y)
/usr/local/lib/python2.7/dist-packages/pandas-0.11.0-py2.7-linux-x86_64.egg/pandas/core/frame.py in __str__(self)
667 if py3compat.PY3:
668 return self.__unicode__()
--> 669 return self.__bytes__()
670
671 def __bytes__(self):
/usr/local/lib/python2.7/dist-packages/pandas-0.11.0-py2.7-linux-x86_64.egg/pandas/core/frame.py in __bytes__(self)
677 """
678 encoding = com.get_option("display.encoding")
--> 679 return self.__unicode__().encode(encoding, 'replace')
680
681 def __unicode__(self):
/usr/local/lib/python2.7/dist-packages/pandas-0.11.0-py2.7-linux-x86_64.egg/pandas/core/frame.py in __unicode__(self)
692 # This needs to compute the entire repr
693 # so don't do it unless rownum is bounded
--> 694 fits_horizontal = self._repr_fits_horizontal_()
695
696 if fits_vertical and fits_horizontal:
/usr/local/lib/python2.7/dist-packages/pandas-0.11.0-py2.7-linux-x86_64.egg/pandas/core/frame.py in _repr_fits_horizontal_(self)
652 d=d.iloc[:min(max_rows, height,len(d))]
653
--> 654 d.to_string(buf=buf)
655 value = buf.getvalue()
656 repr_width = max([len(l) for l in value.split('\n')])
/usr/local/lib/python2.7/dist-packages/pandas-0.11.0-py2.7-linux-x86_64.egg/pandas/core/frame.py in to_string(self, buf, columns, col_space, colSpace, header, index, na_rep, formatters, float_format, sparsify, nanRep, index_names, justify, force_unicode, line_width)
1489 header=header, index=index,
1490 line_width=line_width)
-> 1491 formatter.to_string()
1492
1493 if buf is None:
/usr/local/lib/python2.7/dist-packages/pandas-0.11.0-py2.7-linux-x86_64.egg/pandas/core/format.py in to_string(self, force_unicode)
312 text = info_line
313 else:
--> 314 strcols = self._to_str_columns()
315 if self.line_width is None:
316 text = adjoin(1, *strcols)
/usr/local/lib/python2.7/dist-packages/pandas-0.11.0-py2.7-linux-x86_64.egg/pandas/core/format.py in _to_str_columns(self)
265 for i, c in enumerate(self.columns):
266 if self.header:
--> 267 fmt_values = self._format_col(i)
268 cheader = str_columns[i]
269
/usr/local/lib/python2.7/dist-packages/pandas-0.11.0-py2.7-linux-x86_64.egg/pandas/core/format.py in _format_col(self, i)
403 float_format=self.float_format,
404 na_rep=self.na_rep,
--> 405 space=self.col_space)
406
407 def to_html(self, classes=None):
/usr/local/lib/python2.7/dist-packages/pandas-0.11.0-py2.7-linux-x86_64.egg/pandas/core/format.py in format_array(values, formatter, float_format, na_rep, digits, space, justify)
1319 justify=justify)
1320
-> 1321 return fmt_obj.get_result()
1322
1323
/usr/local/lib/python2.7/dist-packages/pandas-0.11.0-py2.7-linux-x86_64.egg/pandas/core/format.py in get_result(self)
1335
1336 def get_result(self):
-> 1337 fmt_values = self._format_strings()
1338 return _make_fixed_width(fmt_values, self.justify)
1339
/usr/local/lib/python2.7/dist-packages/pandas-0.11.0-py2.7-linux-x86_64.egg/pandas/core/format.py in _format_strings(self)
1362
1363 print "vals:", vals
-> 1364 is_float = lib.map_infer(vals, com.is_float) & notnull(vals)
1365 leading_space = is_float.any()
1366
ValueError: operands could not be broadcast together with shapes (2) (2,3)
现在，在解释了我正在创建一个包含重复条目的索引之后，错误的来源就很清楚了。然而，在不知道这一点的情况下，（同样，对于像我这样的新手）要弄清楚为什么会弹出这个异常会更加困难。
这导致我提出几个问题。
- 这真的是熊猫的预期行为吗？是否禁止创建具有重复条目的索引，或者只是禁止对其进行迭代？
- 如果禁止创建这样的索引，那么最初创建它时不应该引发异常吗？
- 如果迭代在某种程度上不正确，那么错误不应该提供更多信息吗？
- 难道我做错了什么？