Are there alternative methods to creating an empty array then filling it in Python?

user_13061992 0
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I am new to Python but I have a decent amount of experience in Java and C, I am trying to create an array of a certain size then fill it with random numbers but no python tutorials about arrays mention methods about doing this (if I search explicitly about wanting that I get results that is not the problem) so I was wondering if that is considered a bad practice in Python and there are alternative ways to accomplishing what I want. Thank you.

numpy-ndarray numpy arrays python
4 Answers

use random or numpy

In [1]: import random

In [2]: [random.random() for i in range(10)]
Out[2]:
[0.8233249954348517,
 0.6215056571076538,
 0.6273288221606772,
 0.12055176228045617,
 0.22782244162965615,
 0.9016145766629989,
 0.04615407289582629,
 0.8870216740449745,
 0.5622680783939463,
 0.9288600326401598]

In [3]: import numpy

In [4]: numpy.random.rand(5)
Out[4]: array([0.9288893 , 0.66600315, 0.82989425, 0.15717061, 0.33444802])

In [5]: list(numpy.random.rand(5))
Out[5]:
[0.46571036413626277,
 0.8268980751228664,
 0.9216520894106733,
 0.26706936577849916,
 0.47348417257319697]
user_11314570

Still to new to comment on @icejoywoo post ^

list are basically arrays for most purposes.

list comprehension is the easiest way to fill an array with lots of things

[ returnVal for i in range(10)]

any for loop or iterator will work return value itself can be a function

x= [None for i in range(10)]
[None,None..None]

x= [x**2 for i in range(10)]
[0,1,4..81]

y = lambda a: int((a**.5)*100)
x= [y(i) for i in range(10)]
[0, 100, 141, 173, 200, 223, 244, 264, 282, 300]
user_151951190

You can use the choices function from random and give it a k argument (number of values to choose):

>>> from random import choices
>>> choices(range(10), k=5)
[1, 8, 6, 9, 8]
user_22408070

Generally, numpy is the memory efficient and fastest way to work with arrays, especially when doing more complex things.

You can generate n random numbers like so

import numpy as np

# how many random numbers you want 
n = 10

# create your array
array = np.random.rand(n)

You can also use a list comprehension to natively create lists, sets, dicts, etc in one beautiful Pythonic line. See section 5.1.3 of the docs

This is often the go to thing and you will be using these a lot.

For your example we can also use Python’s built on random package

import random

# range here is a generator for values 0 to n-1
# array is created by a list comprehension
array = [random.random() for i in range(n)]
user_51252640
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