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NumPy: Access an array by column

NumPy: Array Object Exercise-81 with Solution

Write a NumPy program to access an array by column.

Pictorial Presentation:

Pandas NumPy: Access an array by column.

Sample Solution:

Python Code:

import numpy as np
x= np.arange(9).reshape(3,3)
print("Original array elements:")
print(x)
print("Access an array by column:")
print("First column:")
print(x[:,0])
print("Second column:")
print(x[:,1])
print("Third column:")
print(x[:,2])

Sample Output:

Original array elements:
[[0 1 2]
 [3 4 5]
 [6 7 8]]
Access an array by column:
First column:
[0 3 6]
Second column:
[1 4 7]
Third column:
[2 5 8]

Python Code Editor:

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Previous: Write a NumPy program to convert a NumPy array into Python list structure.
Next: Write a NumPy program to convert a numpy array of float values to a numpy array of integer values.

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Python: Tips of the Day

Python: Kwargs

**kwargs and *args are function arguments that can be very useful.

They are quite underused and often under-understood as well.

Let's try to explain what kwargs are and how to use them.

  • While *args are used to pass arguments at an unknown amount to functions, **kwargs are used to do the same but with named arguments.
  • So, if *args is a list being passed as an argument, you can think of **kwargs as a dictionary that's being passed as an argument to a function.
  • You can use arguments as you wish as long as you follow the correct order which is: arg1, arg2, *args, **kwargs. It's okay to use only one of those but you can't mix the order, for instance, you can't have: function(**kwargs, arg1), that'd be a major faux pas in Python.
  • Another example: You can do function(*args,**kwargs) since it follows the correct order.
  • Here is an example. Let's say satelites are given with their names and weight in tons in dictionary format. Code prints their weight as kilograms along with their names.
def payloads(**kwargs):
    for key, value in kwargs.items():
        print( key+" |||", float(value)*100)
payloads(NavSat1 = '2.5', BaysatG2 = '4')

Output:

NavSat1 ||| 250.0
BaysatG2 ||| 400.0

Since the function above would work for any number of dictionary keys, **kwargs makes perfect sense rather than passing arguments with a fixed amount.

def payloads(**kwargs):
    for key, value in kwargs.items():
        print( key+" |||", float(value)*100)

sats={"Tx211":"3", "V1":"0.50"}
payloads(**sats)

Output:

Tx211 ||| 300.0
V1 ||| 50.0