CODEWITHSUNDEEP
pythonlistselectrandom
O.rka
O.rka

Reputation: 30737

Select 50 items from list at random

I have a function which reads a list of items from a file. How can I select only 50 items from the list randomly to write to another file?

def randomizer(input, output='random.txt'):
    query = open(input).read().split()
    out_file = open(output, 'w')
    
    random.shuffle(query)
    
    for item in query:
        out_file.write(item + '\n')

For example, if the total randomization file was

random_total = ['9', '2', '3', '1', '5', '6', '8', '7', '0', '4']

and I would want a random set of 3, the result could be

random = ['9', '2', '3']

How can I select 50 from the list that I randomized?

Even better, how could I select 50 at random from the original list?

Upvotes: 208

Views: 215161

Answers (5)

John La Rooy
John La Rooy

Reputation: 304375

If the list is in random order, you can just take the first 50.

Otherwise, use

import random
random.sample(the_list, 50)

random.sample help text:

sample(self, population, k) method of random.Random instance
    Chooses k unique random elements from a population sequence.
    
    Returns a new list containing elements from the population while
    leaving the original population unchanged.  The resulting list is
    in selection order so that all sub-slices will also be valid random
    samples.  This allows raffle winners (the sample) to be partitioned
    into grand prize and second place winners (the subslices).
    
    Members of the population need not be hashable or unique.  If the
    population contains repeats, then each occurrence is a possible
    selection in the sample.
    
    To choose a sample in a range of integers, use xrange as an argument.
    This is especially fast and space efficient for sampling from a
    large population:   sample(xrange(10000000), 60)

Upvotes: 415

A Suresh
A Suresh

Reputation: 129

  1. we have 3 samples ('orange','mango','apple'). Created series, should contain 7 elements & randomly selected from list.

    random.choice
    import random

import numpy as np

fruits = ['orange','mango','apple']

np.random.choice(fruits, 7, replace=True)

    Output

    array(['orange', 'mango', 'apple', 'orange', 'orange', 'mango', 'apple'],
      dtype='<U6')

  2. Random selection from list (less than 3 values)

    random.sample
    import random

random.sample(fruits, 3)

Upvotes: 3

AlketCecaj
AlketCecaj

Reputation: 117

Say your list has 100 elements and you want to pick 50 of them in a random way. Here are the steps to follow:

  1. Import the libraries
  2. Create the seed for random number generator, I have put it at 2
  3. Prepare a list of numbers from which to pick up in a random way
  4. Make the random choices from the numbers list

Code:

from random import seed
from random import choice

seed(2)
numbers = [i for i in range(100)]

print(numbers)

for _ in range(50):
    selection = choice(numbers)
    print(selection)

Upvotes: -4

Moein
Moein

Reputation: 1730

I think random.choice() is a better option.

import numpy as np

mylist = [13,23,14,52,6,23]

np.random.choice(mylist, 3, replace=False)

the function returns an array of 3 randomly chosen values from the list

Upvotes: 47

Mani
Mani

Reputation: 5648

One easy way to select random items is to shuffle then slice. 

import random
a = [1,2,3,4,5,6,7,8,9]
random.shuffle(a)
print a[:4] # prints 4 random variables

Upvotes: 52

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