The best answers to the question “Generate 'n' unique random numbers within a range [duplicate]” in the category Dev.

__QUESTION__:

I know how to generate a random number within a range in Python.

```
random.randint(numLow, numHigh)
```

And I know I can put this in a loop to generate n amount of these numbers

```
for x in range (0, n):
listOfNumbers.append(random.randint(numLow, numHigh))
```

However, I need to make sure each number in that list is unique. Other than a load of conditional statements, is there a straightforward way of generating n number of unique random numbers?

The important thing is that each number in the list is different to the others..

So

[12, 5, 6, 1] = good

But

[12, 5, 5, 1] = bad, because the number 5 occurs twice.

__ANSWER__:

Generate the range of data first and then shuffle it like this

```
import random
data = range(numLow, numHigh)
random.shuffle(data)
print data
```

By doing this way, you will get all the numbers in the particular range but in a random order.

But you can use `random.sample`

to get the number of elements you need, from a range of numbers like this

```
print random.sample(range(numLow, numHigh), 3)
```

__ANSWER__:

If you just need sampling without replacement:

```
>>> import random
>>> random.sample(range(1, 100), 3)
[77, 52, 45]
```

random.sample takes a population and a sample size `k`

and returns `k`

random members of the population.

If you have to control for the case where `k`

is larger than `len(population)`

, you need to be prepared to catch a `ValueError`

:

```
>>> try:
... random.sample(range(1, 2), 3)
... except ValueError:
... print('Sample size exceeded population size.')
...
Sample size exceeded population size
```

__ANSWER__:

You could use the `random.sample`

function from the standard library to select *k* elements from a *population*:

```
import random
random.sample(range(low, high), n)
```

In case of a rather large range of possible numbers, you could use `itertools.islice`

with an infinite random generator:

```
import itertools
import random
def random_gen(low, high):
while True:
yield random.randrange(low, high)
gen = random_gen(1, 100)
items = list(itertools.islice(gen, 10)) # Take first 10 random elements
```

After the question update it is now clear that you need *n* distinct (unique) numbers.

```
import itertools
import random
def random_gen(low, high):
while True:
yield random.randrange(low, high)
gen = random_gen(1, 100)
items = set()
# Try to add elem to set until set length is less than 10
for x in itertools.takewhile(lambda x: len(items) < 10, gen):
items.add(x)
```

__ANSWER__:

You could add to a `set`

until you reach `n`

:

```
setOfNumbers = set()
while len(setOfNumbers) < n:
setOfNumbers.add(random.randint(numLow, numHigh))
```

Be careful of having a smaller range than will fit in `n`

. It will loop forever, unable to find new numbers to insert up to `n`