data frame

[Peter Otten]

Val Krem via Python-list wrote:

> Hi all,
> 
> #!/usr/bin/env python
> import sys
> import csv
> import numpy as np
> import pandas as  pd
> 
> a= pd.read_csv("s1.csv")
> print(a)
> 
>      size   w1   h1
> 0  512  214   26
> 1  123  250   34
> 2  234  124   25
> 3  334  213   43
> 4  a45  223   32
> 5  a12  214   26
> 
> I wanted to create a new column by adding the two column values
> as follows
> 
> a['test'] = a['w1'] + a['h1']
> 
> Traceback (most recent call last):
> File
> "/data/apps/Intel/intelpython35/lib/python3.5/site-
packages/pandas/indexes/base.py",
> line 2104, in get_loc return self._engine.get_loc(key) File
> "pandas/index.pyx", line 139, in pandas.index.IndexEngine.get_loc
> (pandas/index.c:4152) File "pandas/index.pyx", line 161, in
> pandas.index.IndexEngine.get_loc (pandas/index.c:4016) File
> "pandas/src/hashtable_class_helper.pxi", line 732, in
> pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:13153)
> File "pandas/src/hashtable_class_helper.pxi", line 740, in
> pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:13107)
> KeyError: 'w1'
> 
> During handling of the above exception, another exception occurred:
> 
> Traceback (most recent call last):
> File "tt.py", line 16, in <module>
> a['test']=a['w1'] + a['h1']
> 
> File "pandas/src/hashtable_class_helper.pxi", line 740, in
> pandas.hashtable.PyObjectHashTable.get_item (pandas/hashtable.c:13107)
> KeyError: 'w1'
> 
> Can someone help me what the problem is?
> 
> Thank you in advance

Have a look at a.keys(). I suspect that the column name has extra space:

>>> pd.read_csv("s1.csv").keys()
Index([u'size', u' w1', u' h1'], dtype='object')

I that's what you see you can fix it by reading the csv with 
skipinitialspace=True:

>>> pd.read_csv("s1.csv", skipinitialspace=True).keys()
Index([u'size', u'w1', u'h1'], dtype='object')