Generate a set of sorted random numbers from a spe

Question

I'd like to generate a set of x unique random numbers and sort them in Python. For example: range(1000, 10000) x = 100

I've figured out to import random and use the random.randrange method, then loop to get 100 random numbers and in the end sort them.

However, I don't know how to get unique numbers (such that they do not repeat) - should I validate each and every loop? Or is there any other easier way how to do it? And how should I sort them?

Thanks y'all!

Answer 1

more_itertools implements the random_combinations itertools recipe, which returns r sorted random numbers, if given a sorted input.

import more_itertools as mit

mit.random_combination(range(1000, 10000), r=100)
# (1016, 1112, 1233, 1367, 1446, 1460, 1518, 1807, 1832, 1956, ...)

This is unlike random.sample, which returns an unsorted result.

---

Details

Looking at the recipe, we can see why this order is established.

From itertools recipes:

def random_combination(iterable, r):
    """Return a random *r* length subsequence of the elements in *iterable*.
        >>> random_combination(range(5), 3)  # doctest:+SKIP
        (2, 3, 4)
    This equivalent to taking a random selection from
    ``itertools.combinations(iterable, r)``.
    """
    pool = tuple(iterable)
    n = len(pool)
    indices = sorted(sample(range(n), r))
    return tuple(pool[i] for i in indices)

range() is inherently sorted and becomes the pool from which random elements are selected. Although the indices are randomly selected, they are later sorted. Since the pool and indices are both sorted, the results are also sorted.

In summary, this does the same as @Volatility's answer, except the sorting is handled for you.

Cavaet: random_combinations requires the length of the iterable to exceed the value of r, otherwise an error is raised.

Answer 2

Use random.sample

numbers = random.sample(xrange(1000, 10000), 100)  # or `range` in Python 3

The sorting part is easy - use the list.sort method.

numbers.sort()

By default this will sort it from smallest number to largest, but it takes an optional key argument which determines what to sort it on.

There is also a sorted function which doesn't modify a list in-place, but rather returns a sorted list.

numbers_sorted = sorted(numbers)

This also has an optional key argument.