Read specific columns with pandas or other python module

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Question :

Read specific columns with pandas or other python module

I have a csv file from this webpage.
I want to read some of the columns in the downloaded file (the csv version can be downloaded in the upper right corner).

Let’s say I want 2 columns:

  • 59 which in the header is star_name
  • 60 which in the header is ra.

However, for some reason the authors of the webpage sometimes decide to move the columns around.

In the end I want something like this, keeping in mind that values can be missing.

data = #read data in a clever way
names = data['star_name']
ras = data['ra']

This will prevent my program to malfunction when the columns are changed again in the future, if they keep the name correct.

Until now I have tried various ways using the csv module and resently the pandas module. Both without any luck.

EDIT (added two lines + the header of my datafile. Sorry, but it’s extremely long.)

# name, mass, mass_error_min, mass_error_max, radius, radius_error_min, radius_error_max, orbital_period, orbital_period_err_min, orbital_period_err_max, semi_major_axis, semi_major_axis_error_min, semi_major_axis_error_max, eccentricity, eccentricity_error_min, eccentricity_error_max, angular_distance, inclination, inclination_error_min, inclination_error_max, tzero_tr, tzero_tr_error_min, tzero_tr_error_max, tzero_tr_sec, tzero_tr_sec_error_min, tzero_tr_sec_error_max, lambda_angle, lambda_angle_error_min, lambda_angle_error_max, impact_parameter, impact_parameter_error_min, impact_parameter_error_max, tzero_vr, tzero_vr_error_min, tzero_vr_error_max, K, K_error_min, K_error_max, temp_calculated, temp_measured, hot_point_lon, albedo, albedo_error_min, albedo_error_max, log_g, publication_status, discovered, updated, omega, omega_error_min, omega_error_max, tperi, tperi_error_min, tperi_error_max, detection_type, mass_detection_type, radius_detection_type, alternate_names, molecules, star_name, ra, dec, mag_v, mag_i, mag_j, mag_h, mag_k, star_distance, star_metallicity, star_mass, star_radius, star_sp_type, star_age, star_teff, star_detected_disc, star_magnetic_field
11 Com b,19.4,1.5,1.5,,,,326.03,0.32,0.32,1.29,0.05,0.05,0.231,0.005,0.005,0.011664,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1,2008,2011-12-23,94.8,1.5,1.5,2452899.6,1.6,1.6,Radial Velocity,,,,,11 Com,185.1791667,17.7927778,4.74,,,,,110.6,-0.35,2.7,19.0,G8 III,,4742.0,,
11 UMi b,10.5,2.47,2.47,,,,516.22,3.25,3.25,1.54,0.07,0.07,0.08,0.03,0.03,0.012887,,,,,,,,,,,,,,,,,,,,,,,,,,,,,1,2009,2009-08-13,117.63,21.06,21.06,2452861.05,2.06,2.06,Radial Velocity,,,,,11 UMi,229.275,71.8238889,5.02,,,,,119.5,0.04,1.8,24.08,K4III,1.56,4340.0,,

Answer #1:

An easy way to do this is using the pandas library like this.

import pandas as pd
fields = ['star_name', 'ra']

df = pd.read_csv('data.csv', skipinitialspace=True, usecols=fields)
# See the keys
print df.keys()
# See content in 'star_name'
print df.star_name

The problem here was the skipinitialspace which remove the spaces in the header. So ‘ star_name’ becomes ‘star_name’

Answer #2:

According to the latest pandas documentation you can read a csv file selecting only the columns which you want to read.

import pandas as pd

df = pd.read_csv('some_data.csv', usecols = ['col1','col2'], low_memory = True)

Here we use usecols which reads only selected columns in a dataframe.

We are using low_memory so that we Internally process the file in chunks.

Answer #3:

Got a solution to above problem in a different way where in although i would read entire csv file, but would tweek the display part to show only the content which is desired.

import pandas as pd

df = pd.read_csv('data.csv', skipinitialspace=True)
print df[['star_name', 'ra']]

This one could help in some of the scenario’s in learning basics and filtering data on the basis of columns in dataframe.

Answered By: Decision Scientist

Answer #4:

Above answers are in python2. So for python 3 users I am giving this answer. You can use the bellow code:

import pandas as pd
fields = ['star_name', 'ra']

df = pd.read_csv('data.csv', skipinitialspace=True, usecols=fields)
# See the keys
# See content in 'star_name'
Answered By: frp farhan

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