python - 值错误 : Wrong number of items passed - Meaning and suggestions?

Question

我收到错误: ValueError:错误的项目数通过了 3，位置意味着 1，我正在努力弄清楚从哪里以及如何开始解决问题。

我不太明白错误的含义；这让我很难排除故障。我还在 Jupyter Notebook 中包含了触发错误的代码块。

数据很难附加；所以我不是在寻找任何人来尝试为我重新创建这个错误。我只是在寻找有关如何解决此错误的反馈。

KeyError                                  Traceback (most recent call last)
C:\Users\brennn1\AppData\Local\Continuum\Anaconda3\lib\site-packages\pandas\indexes\base.py in get_loc(self, key, method, tolerance)
   1944             try:
-> 1945                 return self._engine.get_loc(key)
   1946             except KeyError:

pandas\index.pyx in pandas.index.IndexEngine.get_loc (pandas\index.c:4154)()

pandas\index.pyx in pandas.index.IndexEngine.get_loc (pandas\index.c:4018)()

pandas\hashtable.pyx in pandas.hashtable.PyObjectHashTable.get_item (pandas\hashtable.c:12368)()

pandas\hashtable.pyx in pandas.hashtable.PyObjectHashTable.get_item (pandas\hashtable.c:12322)()

KeyError: 'predictedY'

During handling of the above exception, another exception occurred:

KeyError                                  Traceback (most recent call last)
C:\Users\brennn1\AppData\Local\Continuum\Anaconda3\lib\site-packages\pandas\core\internals.py in set(self, item, value, check)
   3414         try:
-> 3415             loc = self.items.get_loc(item)
   3416         except KeyError:

C:\Users\brennn1\AppData\Local\Continuum\Anaconda3\lib\site-packages\pandas\indexes\base.py in get_loc(self, key, method, tolerance)
   1946             except KeyError:
-> 1947                 return self._engine.get_loc(self._maybe_cast_indexer(key))
   1948 

pandas\index.pyx in pandas.index.IndexEngine.get_loc (pandas\index.c:4154)()

pandas\index.pyx in pandas.index.IndexEngine.get_loc (pandas\index.c:4018)()

pandas\hashtable.pyx in pandas.hashtable.PyObjectHashTable.get_item (pandas\hashtable.c:12368)()

pandas\hashtable.pyx in pandas.hashtable.PyObjectHashTable.get_item (pandas\hashtable.c:12322)()

KeyError: 'predictedY'

During handling of the above exception, another exception occurred:

ValueError                                Traceback (most recent call last)
<ipython-input-95-476dc59cd7fa> in <module>()
     26     return gp, results
     27 
---> 28 gp_dailyElectricity, results_dailyElectricity = predictAll(3, 0.04, trainX_dailyElectricity, trainY_dailyElectricity, testX_dailyElectricity, testY_dailyElectricity, testSet_dailyElectricity, 'Daily Electricity')

<ipython-input-95-476dc59cd7fa> in predictAll(theta, nugget, trainX, trainY, testX, testY, testSet, title)
      8 
      9     results = testSet.copy()
---> 10     results['predictedY'] = predictedY
     11     results['sigma'] = sigma
     12 

C:\Users\brennn1\AppData\Local\Continuum\Anaconda3\lib\site-packages\pandas\core\frame.py in __setitem__(self, key, value)
   2355         else:
   2356             # set column
-> 2357             self._set_item(key, value)
   2358 
   2359     def _setitem_slice(self, key, value):

C:\Users\brennn1\AppData\Local\Continuum\Anaconda3\lib\site-packages\pandas\core\frame.py in _set_item(self, key, value)
   2422         self._ensure_valid_index(value)
   2423         value = self._sanitize_column(key, value)
-> 2424         NDFrame._set_item(self, key, value)
   2425 
   2426         # check if we are modifying a copy

C:\Users\brennn1\AppData\Local\Continuum\Anaconda3\lib\site-packages\pandas\core\generic.py in _set_item(self, key, value)
   1462 
   1463     def _set_item(self, key, value):
-> 1464         self._data.set(key, value)
   1465         self._clear_item_cache()
   1466 

C:\Users\brennn1\AppData\Local\Continuum\Anaconda3\lib\site-packages\pandas\core\internals.py in set(self, item, value, check)
   3416         except KeyError:
   3417             # This item wasn't present, just insert at end
-> 3418             self.insert(len(self.items), item, value)
   3419             return
   3420 

C:\Users\brennn1\AppData\Local\Continuum\Anaconda3\lib\site-packages\pandas\core\internals.py in insert(self, loc, item, value, allow_duplicates)
   3517 
   3518         block = make_block(values=value, ndim=self.ndim,
-> 3519                            placement=slice(loc, loc + 1))
   3520 
   3521         for blkno, count in _fast_count_smallints(self._blknos[loc:]):

C:\Users\brennn1\AppData\Local\Continuum\Anaconda3\lib\site-packages\pandas\core\internals.py in make_block(values, placement, klass, ndim, dtype, fastpath)
   2516                      placement=placement, dtype=dtype)
   2517 
-> 2518     return klass(values, ndim=ndim, fastpath=fastpath, placement=placement)
   2519 
   2520 # TODO: flexible with index=None and/or items=None

C:\Users\brennn1\AppData\Local\Continuum\Anaconda3\lib\site-packages\pandas\core\internals.py in __init__(self, values, placement, ndim, fastpath)
     88             raise ValueError('Wrong number of items passed %d, placement '
     89                              'implies %d' % (len(self.values),
---> 90                                              len(self.mgr_locs)))
     91 
     92     @property

ValueError: Wrong number of items passed 3, placement implies 1

我的代码如下:

def predictAll(theta, nugget, trainX, trainY, testX, testY, testSet, title):

    gp = gaussian_process.GaussianProcess(theta0=theta, nugget =nugget)
    gp.fit(trainX, trainY)

    predictedY, MSE = gp.predict(testX, eval_MSE = True)
    sigma = np.sqrt(MSE)

    results = testSet.copy()
    results['predictedY'] = predictedY
    results['sigma'] = sigma

    print ("Train score R2:", gp.score(trainX, trainY))
    print ("Test score R2:", sklearn.metrics.r2_score(testY, predictedY))

    plt.figure(figsize = (9,8))
    plt.scatter(testY, predictedY)
    plt.plot([min(testY), max(testY)], [min(testY), max(testY)], 'r')
    plt.xlim([min(testY), max(testY)])
    plt.ylim([min(testY), max(testY)])
    plt.title('Predicted vs. observed: ' + title)
    plt.xlabel('Observed')
    plt.ylabel('Predicted')
    plt.show()

    return gp, results

gp_dailyElectricity, results_dailyElectricity = predictAll(3, 0.04, trainX_dailyElectricity, trainY_dailyElectricity, testX_dailyElectricity, testY_dailyElectricity, testSet_dailyElectricity, 'Daily Electricity')

Answer 1

一般来说，错误 ValueError: Wrong number of items passed 3, placement imply 1 表明您试图将太多鸽子放入太少的鸽笼中。在这种情况下，等式右边的值

results['predictedY'] = predictY

试图将 3 个“东西”放入一个只允许一个的容器中。因为左侧是数据框列，并且可以在该(列)维度上接受多个项目，所以您应该看到另一个维度上的项目太多。

在这里，您似乎正在使用 sklearn 进行建模，这就是 gaussian_process.GaussianProcess() 的来源(我猜，但如果这是错误的，请纠正我并修改问题) .

现在，您在此处生成 y 的预测值:

predictedY, MSE = gp.predict(testX, eval_MSE = True)

但是，正如我们从 the documentation for GaussianProcess 中看到的那样, predict() 返回两项。第一个是y，它是类似数组的(强调我的)。这意味着它可以有多个维度，或者，对于像我这样头脑粗的人来说，它可以有多个列——看它可以返回 (n_samples, n_targets) 哪个，取决于 testX，可能是 (1000, 3) (只是为了选择数字)。因此，您的 predictedY 可能有 3 列。

如果是这样，当您尝试将包含三个“列”的内容放入单个数据框列中时，您将传递 3 个仅适合 1 个的项目。