Pandas drop first columns after csv read

Question

Is there a way to reference an object within the line of the instantiation ?

See the following example : I wanted to drop the first column (by index) of a csv file just after reading it (usually pd.to_csv outputs the index as first col) :

df = pd.read_csv(csvfile).drop(self.columns[[0]], axis=1)

I understand self should be placed in the object context but it here describes what I intent to do.

(Of course, doing this operation in two separate lines works perfectly.)

Solution 1

One way is to use pd.DataFrame.iloc:

import pandas as pd
from io import StringIO

mystr = StringIO("""col1,col2,col3
a,b,c
d,e,f
g,h,i
""")

df = pd.read_csv(mystr).iloc[:, 1:]

#   col2 col3
# 0    b    c
# 1    e    f
# 2    h    i

Solution 2

Assuming you know the total number of columns in the dataset, and the indexes you want to remove -

a = range(3)
a.remove(1)
df = pd.read_csv('test.csv', usecols = a)

Here 3 is the total number of columns, and I wanted to remove 2nd column. You can directly write index of columns to use

Comments

[Ti me]

Hi, this works fine and it's a simple single line. thank you.Still I wonder if there is a way to refer to an object on the line it's instantiated...

[jpp]

Don't think so. The problem is the usecols argument for read_csv accepts only array-like input, so [1, 2] is valid input to exclude the iniitial column, but [1:] is not.