錯誤詮釋散點圖

Question

我有這樣一個DF：

Allotment C1  C2  
Annex  1.0 2.0 
Arnstson  1.6 1.4 
Berg   2.1 4.5 
Bjugstad  6.7 6.9 

，我做的C1和C2散點圖，同時與相關Allotment標籤。我這樣做的：

a=df.C1 
b=df.C2 
n=df.Allotment 

    with PdfPages(r'C:\plot.pdf') as pdf: 
      plt.title('PC1 vs. PC2 Scatterplot') 
      plt.xlabel('PC1') 
      plt.ylabel('PC2') 
      plt.scatter(a,b, facecolors='none', s=20, edgecolors='b') 
      # use this portion to annotate each point 
      for i, txt in enumerate(n): 
       plt.annotate(txt, (a[i],b[i]), fontsize=2.5) 
      fig=plt.gcf() 
      pdf.savefig(fig) 
      plt.show() 

但是當我執行這一行刪除Allotments：

df=df[~df['Allotments'] .isin (['Berg', 'Annex'])] 

並運行相同的代碼，我收到以下錯誤：

Traceback (most recent call last): 

    File "<ipython-input-58-c5ce20451164>", line 1, in <module> 
    runfile('H:/python codes/PC_scatterplots.py', wdir='H:/python codes') 

    File "C:\Users\spotter\AppData\Local\Continuum\Anaconda\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 685, in runfile 
    execfile(filename, namespace) 

    File "C:\Users\spotter\AppData\Local\Continuum\Anaconda\lib\site-packages\spyderlib\widgets\externalshell\sitecustomize.py", line 71, in execfile 
    exec(compile(scripttext, filename, 'exec'), glob, loc) 

    File "H:/python codes/PC_scatterplots.py", line 64, in <module> 
    plt.annotate(txt, (a[i],b[i]), fontsize=2.5) 

    File "C:\Users\spotter\AppData\Local\Continuum\Anaconda\lib\site-packages\pandas\core\series.py", line 521, in __getitem__ 
    result = self.index.get_value(self, key) 

    File "C:\Users\spotter\AppData\Local\Continuum\Anaconda\lib\site-packages\pandas\core\index.py", line 1595, in get_value 
    return self._engine.get_value(s, k) 

    File "pandas\index.pyx", line 100, in pandas.index.IndexEngine.get_value (pandas\index.c:3113) 

    File "pandas\index.pyx", line 108, in pandas.index.IndexEngine.get_value (pandas\index.c:2844) 

    File "pandas\index.pyx", line 154, in pandas.index.IndexEngine.get_loc (pandas\index.c:3704) 

    File "pandas\hashtable.pyx", line 375, in pandas.hashtable.Int64HashTable.get_item (pandas\hashtable.c:7224) 

    File "pandas\hashtable.pyx", line 381, in pandas.hashtable.Int64HashTable.get_item (pandas\hashtable.c:7162) 

KeyError: 9L 

Answer 1

當您enumerate,i是一個新開始的索引，起始於0，而a和b保留索引從df。

In [83] df 

    Allotment C1 C2 
0 Annex  1.0  2.0 
1 Arnston  1.6  1.4 
2 Berg  2.1  4.5 
3 Bjugstad 6.7  6.9 

In [84]: a=df.C1 
     b=df.C2 
     n=df.Allotment 

In [85]: for i, txt in enumerate(n): 
      print i,txt 
0 Annex 
1 Arnston 
2 Berg 
3 Bjugstad 

但是，當您將df分配給子集時，原始索引仍然存在。

df=df[~df['Allotment'].isin (['Berg', 'Annex'])] 

a=df.C1 
b=df.C2 
n=df.Allotment 

In [86]: a 
Out[86]: 
    1 1.6 
    3 6.7 

In [87]: for i, txt in enumerate(n): 
      print i,txt 
      print a[i] #doesn't exist 

重複次數類似的錯誤到你：

0 Arnston 

--------------------------------------------------------------------------- 
KeyError         Traceback (most recent call last) 
<ipython-input-23-b79737b511ee> in <module>() 
     1 for i, txt in enumerate(n): 
     2  print i,txt 
----> 3  print a[i] 

/home/kevin/anaconda2/lib/python2.7/site-packages/pandas/core/series.pyc in __getitem__(self, key) 
    549  def __getitem__(self, key): 
    550   try: 
--> 551    result = self.index.get_value(self, key) 
    552 
    553    if not np.isscalar(result): 

/home/kevin/anaconda2/lib/python2.7/site-packages/pandas/core/index.pyc in get_value(self, series, key) 
    1721 
    1722   try: 
-> 1723    return self._engine.get_value(s, k) 
    1724   except KeyError as e1: 
    1725    if len(self) > 0 and self.inferred_type in ['integer','boolean']: 

pandas/index.pyx in pandas.index.IndexEngine.get_value (pandas/index.c:3204)() 

pandas/index.pyx in pandas.index.IndexEngine.get_value (pandas/index.c:2903)() 

pandas/index.pyx in pandas.index.IndexEngine.get_loc (pandas/index.c:3843)() 

pandas/hashtable.pyx in pandas.hashtable.Int64HashTable.get_item (pandas/hashtable.c:6525)() 

pandas/hashtable.pyx in pandas.hashtable.Int64HashTable.get_item (pandas/hashtable.c:6463)() 

KeyError: 0 

所以，你可以使用.iloc THX Jezzamon，它正確繪製。

for i, txt in enumerate(n): 
    print a.iloc[i] 
1.6 
6.7