Python Forum

Hello all, this is my first time here so apologies if something is missed or in the wrong place.

I have recently started to learn to code and I am struggling with writing a function that will allow me to get all the data from a column in a data set by calling a function with inputs of the data set and a column number. I am completely stuck and any help would be appreciated.

My function starts like this:

def get_column(data, col_num): 

I already have the data so that does not need to be imported and col_num is the input to which I would type, for example:

print(get_column(data, 5))

and it would return the 4th column.

Thanks.

What is data? You call it a data set, but I am not familiar with that data type. Is it a Pandas DataFrame? Provide more information about your data please. If possible provide the code that creates data

(Oct-06-2021, 06:08 PM)deanhystad Wrote: [ -> ]What is data? You call it a data set, but I am not familiar with that data type. Is it a Pandas DataFrame? Provide more information about your data please. If possible provide the code that creates data

Sorry, the data is a .csv file. I am not currently using Pandas but I am using Numpy

Could you please provide code that shows how you are reading the csv file.

if data is a 2D numpy array, getting column 2 is as simple as: column=data[:, 2]:

import numpy as np

data = np.array([[1, 2, 3, 4], [5, 6, 7, 8], [9, 10, 11, 12]])

# Print the columns one at a time.
for i in range(len(data[0])):
    print(i, data[:, i])

Output:
0 [1 5 9]
1 [ 2  6 10]
2 [ 3  7 11]
3 [ 4  8 12]

I am reading the file such that

data = np.loadtxt('data.csv', delimiter = ',', skiprows = 1)

I need my function to get that column of data when I call the function,

e.g when I do print(get_column(data, 3)) it should call the function and get me the data from column 4 only

If your data.csv file looks like mine, you can get columns the same way. No need to write a function.

import numpy as np

# data.csv looks like this: "these, are, column, headers\n1, 2, 3, 4\n5, 6, 7, 8\n9, 10, 11, 12"
data = np.loadtxt('data.csv', delimiter = ',', skiprows = 1)
print(f'np Array\n{data}\n\nColumns')

# Print the columns one at a time.
for i in range(len(data[0])):
    print(i, data[:, i])  # You don't need a function.  This does all you need

Output:
np Array
[[ 1.  2.  3.  4.]
 [ 5.  6.  7.  8.]
 [ 9. 10. 11. 12.]]

Columns
0 [1. 5. 9.]
1 [ 2.  6. 10.]
2 [ 3.  7. 11.]
3 [ 4.  8. 12.]

But if you need to write a function.

def getColumn(data, column):
    return data[:, column]

Thank you so much for the help! It works perfectly now!