Error Annotating Scatterplot

Question

I have a df like this:

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

and I am making a scatter plot of C1 and C2 while labeling with the associated Allotment. I am doing this like this:

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()

but when I implement this line to remove Allotments:

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

and run the same code I get the following error:

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

Kevin · Accepted Answer · 2016-02-19 23:00:13Z

When you enumerate, i is a newly initiated index starting at 0, while a and b retain the indices from the 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

But when you assign df to the subset, the original indices remain.

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

Replicates similar error to yours:

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

So you could use .iloc thx Jezzamon, it plots correctly.

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

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