data frame

Fri Dec 23 16:08:28 EST 2016

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')