python - read csv files pandas slice arrays -

i'm python newbie , having trouble reading csv pandas , working it. here bit of csv file:

a   b 1   56 2   76 3   23 4   45 5   54 6   65 7   22 

and python code:

import numpy np import pandas pd  math import exp math import sqrt  g = pd.dataframe.from_csv('test.csv')  = g.iloc[2:4,1] print(a) 

i following error:

indexerror: index 1 out of bounds axis 0 size 1 

i've tried:

a = g.iloc[2:4,'b'] 

and many other permutations defining columns , rows.

also when print g, following:

             b              2015-05-01  56 2015-05-02  76 2015-05-03  23 2015-05-04  45 2015-05-05  54 2015-05-06  65 2015-05-07  22 

i can't understand why , b not aligned.

i'm using example, in general i'd read in large csv files , perform operations on aspects of matrix.

any appreciated.

firstly dataframe.from_csv whilst still supported, it's better use top level read_csv instead supports more functionality.

so this:

a = g.iloc[2:4,1] 

is wrong syntax, want:

a = g.iloc[2:4]['a'] 

secondly, default dataframe.from_csv uses first column index why column 'a' index, if passed index_col=none desired result:

in [6]: pd.dataframe.from_csv(file_path)  out[6]:     b     1  56 2  76 3  23 4  45 5  54 6  65 7  22 in [7]:     pd.dataframe.from_csv(file_path, index_col=none)  out[7]:      b 0  1  56 1  2  76 2  3  23 3  4  45 4  5  54 5  6  65 6  7  22 

correct syntax:

in [9]:    df.iloc[2:4]['a']  out[9]: 2    3 3    4 name: a, dtype: int64 

additionally read_csv default index_col none problem alignment not have happened if had used read_csv.

please check docs on indexing , selecting.

edit

as @jeff suggested , agree jeff, kind of selection ix typical selection method it's behaviour differs iloc in include end row selection unlike iloc:

in [10]:     df.ix[2:4,'a']  out[10]: 2    3 3    4 4    5 name: a, dtype: int64 

so don't know wanted row selection-wise aware of different semantics.

update

note .ix deprecated in future, can achieve same result using .loc:

in [202]: df.loc[2:4,'a']  out[202]: 2    3 3    4 4    5 name: a, dtype: int64