The following code demonstrates if you need to produce the same items. You can also specify how many samples you want to extract.
The sample method 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.
import random as random
random.seed(0) # don't use seed function, if you want different results in each run
print(random.sample(foo,3)) # 3 is the number of sample you want to retrieve
Output:['d', 'e', 'a']
This is the code with a variable that defines the random index:
import random
foo = ['a', 'b', 'c', 'd', 'e']
randomindex = random.randint(0,len(foo)-1)
print (foo[randomindex])
## print (randomindex)
This is the code without the variable:
import random
foo = ['a', 'b', 'c', 'd', 'e']
print (foo[random.randint(0,len(foo)-1)])
And this is the code in the shortest and smartest way to do it:
import random
foo = ['a', 'b', 'c', 'd', 'e']
print(random.choice(foo))
(python 2.7)
import random
my_list = [1, 2, 3, 4, 5]
num_selections = 2
new_list = random.sample(my_list, num_selections)
randIndex = random.sample(range(len(my_list)), n_selections)
randIndex.sort()
new_list = [my_list[i] for i in randIndex]
Duplicate of https://stackoverflow.com/a/49682832/4383027
foo = ['a', 'b', 'c', 'd', 'e']
number_of_samples = 1
In python 2:
random_items = random.sample(population=foo, k=number_of_samples)
In python 3:
random_items = random.choices(population=foo, k=number_of_samples)
If you want to randomly select more than one item from a list, or select an item from a set, I'd recommend using random.sample instead.
import random
group_of_items = {1, 2, 3, 4} # a sequence or set will work here.
num_to_select = 2 # set the number to select here.
list_of_random_items = random.sample(group_of_items, num_to_select)
first_random_item = list_of_random_items[0]
second_random_item = list_of_random_items[1]
If you're only pulling a single item from a list though, choice is less clunky, as using sample would have the syntax random.sample(some_list, 1)[0] instead of random.choice(some_list).
Unfortunately though, choice only works for a single output from sequences (such as lists or tuples). Though random.choice(tuple(some_set)) may be an option for getting a single item from a set.
EDIT: Using Secrets
As many have pointed out, if you require more secure pseudorandom samples, you should use the secrets module:
import secrets # imports secure module.
secure_random = secrets.SystemRandom() # creates a secure random object.
group_of_items = {1, 2, 3, 4} # a sequence or set will work here.
num_to_select = 2 # set the number to select here.
list_of_random_items = secure_random.sample(group_of_items, num_to_select)
first_random_item = list_of_random_items[0]
second_random_item = list_of_random_items[1]
EDIT: Pythonic One-Liner
If you want a more pythonic one-liner for selecting multiple items, you can use unpacking.
import random
first_random_item, second_random_item = random.sample(group_of_items, 2)
if you need the index just use:
import random
foo = ['a', 'b', 'c', 'd', 'e']
print int(random.random() * len(foo))
print foo[int(random.random() * len(foo))]
random.choice does the same:)
numpy solution: numpy.random.choice
For this question, it works the same as the accepted answer (import random; random.choice()), but I added it because the programmer may have imported numpy already (like me)
& also there are some differences between the two methods that may concern your actual use case.
import numpy as np
np.random.choice(foo) # randomly selects a single item
For reproducibility, you can do:
np.random.seed(123)
np.random.choice(foo) # first call will always return 'c'
For samples of one or more items, returned as an array, pass the size argument:
np.random.choice(foo, 5) # sample with replacement (default)
np.random.choice(foo, 5, False) # sample without replacement
This may already be an answer but you could use random.shuffle. Example:
import random
foo = ['a', 'b', 'c', 'd', 'e']
random.shuffle(foo)
If you also need the index, use random.randrange
from random import randrange
random_index = randrange(len(foo))
print(foo[random_index])
This may already be an answer but you could use random.shuffle. Example:
import random
foo = ['a', 'b', 'c', 'd', 'e']
random.shuffle(foo)
How to randomly select an item from a list?
Assume I have the following list:
foo = ['a', 'b', 'c', 'd', 'e']What is the simplest way to retrieve an item at random from this list?
If you want close to truly random, then I suggest secrets.choice from the standard library (New in Python 3.6.):
>>> from secrets import choice # Python 3 only
>>> choice(list('abcde'))
'c'
The above is equivalent to my former recommendation, using a SystemRandom object from the random module with the choice method - available earlier in Python 2:
>>> import random # Python 2 compatible
>>> sr = random.SystemRandom()
>>> foo = list('abcde')
>>> foo
['a', 'b', 'c', 'd', 'e']
And now:
>>> sr.choice(foo)
'd'
>>> sr.choice(foo)
'e'
>>> sr.choice(foo)
'a'
>>> sr.choice(foo)
'b'
>>> sr.choice(foo)
'a'
>>> sr.choice(foo)
'c'
>>> sr.choice(foo)
'c'
If you want a deterministic pseudorandom selection, use the choice function (which is actually a bound method on a Random object):
>>> random.choice
<bound method Random.choice of <random.Random object at 0x800c1034>>
It seems random, but it's actually not, which we can see if we reseed it repeatedly:
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
This is not about whether random.choice is truly random or not. If you fix the seed, you will get the reproducible results -- and that's what seed is designed for. You can pass a seed to SystemRandom, too.
sr = random.SystemRandom(42)
Well, yes you can pass it a "seed" argument, but you'll see that the SystemRandom object simply ignores it:
def seed(self, *args, **kwds):
"Stub method. Not used for a system random number generator."
return None
I propose a script for removing randomly picked up items off a list until it is empty:
Maintain a set and remove randomly picked up element (with choice) until list is empty.
s=set(range(1,6))
import random
while len(s)>0:
s.remove(random.choice(list(s)))
print(s)
Three runs give three different answers:
>>>
set([1, 3, 4, 5])
set([3, 4, 5])
set([3, 4])
set([4])
set([])
>>>
set([1, 2, 3, 5])
set([2, 3, 5])
set([2, 3])
set([2])
set([])
>>>
set([1, 2, 3, 5])
set([1, 2, 3])
set([1, 2])
set([1])
set([])
foo = ['a', 'b', 'c', 'd', 'e']
number_of_samples = 1
In python 2:
random_items = random.sample(population=foo, k=number_of_samples)
In python 3:
random_items = random.choices(population=foo, k=number_of_samples)
How to randomly select an item from a list?
Assume I have the following list:
foo = ['a', 'b', 'c', 'd', 'e']What is the simplest way to retrieve an item at random from this list?
If you want close to truly random, then I suggest secrets.choice from the standard library (New in Python 3.6.):
>>> from secrets import choice # Python 3 only
>>> choice(list('abcde'))
'c'
The above is equivalent to my former recommendation, using a SystemRandom object from the random module with the choice method - available earlier in Python 2:
>>> import random # Python 2 compatible
>>> sr = random.SystemRandom()
>>> foo = list('abcde')
>>> foo
['a', 'b', 'c', 'd', 'e']
And now:
>>> sr.choice(foo)
'd'
>>> sr.choice(foo)
'e'
>>> sr.choice(foo)
'a'
>>> sr.choice(foo)
'b'
>>> sr.choice(foo)
'a'
>>> sr.choice(foo)
'c'
>>> sr.choice(foo)
'c'
If you want a deterministic pseudorandom selection, use the choice function (which is actually a bound method on a Random object):
>>> random.choice
<bound method Random.choice of <random.Random object at 0x800c1034>>
It seems random, but it's actually not, which we can see if we reseed it repeatedly:
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
>>> random.seed(42); random.choice(foo), random.choice(foo), random.choice(foo)
('d', 'a', 'b')
This is not about whether random.choice is truly random or not. If you fix the seed, you will get the reproducible results -- and that's what seed is designed for. You can pass a seed to SystemRandom, too.
sr = random.SystemRandom(42)
Well, yes you can pass it a "seed" argument, but you'll see that the SystemRandom object simply ignores it:
def seed(self, *args, **kwds):
"Stub method. Not used for a system random number generator."
return None
if you need the index just use:
import random
foo = ['a', 'b', 'c', 'd', 'e']
print int(random.random() * len(foo))
print foo[int(random.random() * len(foo))]
random.choice does the same:)
We can also do this using randint.
from random import randint
l= ['a','b','c']
def get_rand_element(l):
if l:
return l[randint(0,len(l)-1)]
else:
return None
get_rand_element(l)
If you want to randomly select more than one item from a list, or select an item from a set, I'd recommend using random.sample instead.
import random
group_of_items = {1, 2, 3, 4} # a sequence or set will work here.
num_to_select = 2 # set the number to select here.
list_of_random_items = random.sample(group_of_items, num_to_select)
first_random_item = list_of_random_items[0]
second_random_item = list_of_random_items[1]
If you're only pulling a single item from a list though, choice is less clunky, as using sample would have the syntax random.sample(some_list, 1)[0] instead of random.choice(some_list).
Unfortunately though, choice only works for a single output from sequences (such as lists or tuples). Though random.choice(tuple(some_set)) may be an option for getting a single item from a set.
EDIT: Using Secrets
As many have pointed out, if you require more secure pseudorandom samples, you should use the secrets module:
import secrets # imports secure module.
secure_random = secrets.SystemRandom() # creates a secure random object.
group_of_items = {1, 2, 3, 4} # a sequence or set will work here.
num_to_select = 2 # set the number to select here.
list_of_random_items = secure_random.sample(group_of_items, num_to_select)
first_random_item = list_of_random_items[0]
second_random_item = list_of_random_items[1]
EDIT: Pythonic One-Liner
If you want a more pythonic one-liner for selecting multiple items, you can use unpacking.
import random
first_random_item, second_random_item = random.sample(group_of_items, 2)
If you also need the index, use random.randrange
from random import randrange
random_index = randrange(len(foo))
print(foo[random_index])
You could just:
from random import randint
foo = ["a", "b", "c", "d", "e"]
print(foo[randint(0,4)])
We can also do this using randint.
from random import randint
l= ['a','b','c']
def get_rand_element(l):
if l:
return l[randint(0,len(l)-1)]
else:
return None
get_rand_element(l)
You could just:
from random import randint
foo = ["a", "b", "c", "d", "e"]
print(foo[randint(0,4)])
The following code demonstrates if you need to produce the same items. You can also specify how many samples you want to extract.
The sample method 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.
import random as random
random.seed(0) # don't use seed function, if you want different results in each run
print(random.sample(foo,3)) # 3 is the number of sample you want to retrieve
Output:['d', 'e', 'a']
As of Python 3.6 you can use the secrets module, which is preferable to the random module for cryptography or security uses.
To print a random element from a list:
import secrets
foo = ['a', 'b', 'c', 'd', 'e']
print(secrets.choice(foo))
To print a random index:
print(secrets.randbelow(len(foo)))
For details, see PEP 506.
This is the code with a variable that defines the random index:
import random
foo = ['a', 'b', 'c', 'd', 'e']
randomindex = random.randint(0,len(foo)-1)
print (foo[randomindex])
## print (randomindex)
This is the code without the variable:
import random
foo = ['a', 'b', 'c', 'd', 'e']
print (foo[random.randint(0,len(foo)-1)])
And this is the code in the shortest and smartest way to do it:
import random
foo = ['a', 'b', 'c', 'd', 'e']
print(random.choice(foo))
(python 2.7)
As of Python 3.6 you can use the secrets module, which is preferable to the random module for cryptography or security uses.
To print a random element from a list:
import secrets
foo = ['a', 'b', 'c', 'd', 'e']
print(secrets.choice(foo))
To print a random index:
print(secrets.randbelow(len(foo)))
For details, see PEP 506.
import random
my_list = [1, 2, 3, 4, 5]
num_selections = 2
new_list = random.sample(my_list, num_selections)
randIndex = random.sample(range(len(my_list)), n_selections)
randIndex.sort()
new_list = [my_list[i] for i in randIndex]
Duplicate of https://stackoverflow.com/a/49682832/4383027
Source: Stackoverflow.com