Random

Overview

Frankie has a built-in random number library — no imports required.

It covers integers, floats, seeding for reproducibility, and collection operations like shuffle and sample.

All functions are wrappers around Python's random module.

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Random Numbers

rand_int(a, b)

Random integer, both ends inclusive

puts rand_int(1, 6)      # dice roll: 1, 2, 3, 4, 5, or 6
puts rand_int(0, 100)    # 0 to 100
puts rand_int(-10, 10)   # -10 to 10

rand_float(a, b)

Random float in range

Returns a float in [a, b) — inclusive on the left, exclusive on the right.

puts rand_float(0.0, 1.0)    # e.g. 0.7493...
puts rand_float(-1.0, 1.0)   # e.g. -0.234...
puts rand_float(0.0, 100.0)  # e.g. 42.17...

rand()

Random float 0.0 to 1.0

puts rand()   # e.g. 0.4217...

rand(n)

Random integer 0 to n-1

puts rand(10)   # 0 to 9 (exclusive upper bound)
puts rand(2)    # 0 or 1 — coin flip

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Reproducibility

rand_seed(n)

Fix the random seed

Seeding produces the same sequence every time — essential for tests, simulations, and reproducible results.

rand_seed(42)
puts rand_int(1, 100)   # always the same value
puts rand_int(1, 100)   # next value in the same sequence
puts rand_int(1, 100)   # and so on

Re-seed to restart the sequence:

rand_seed(42)
a = rand_int(1, 1000)

rand_seed(42)
b = rand_int(1, 1000)

assert_eq(a, b, "same seed produces same value")

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Collections

shuffle(v)

Return a randomly reordered copy

Returns a new vector — does not modify the original.

v = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
puts shuffle(v)    # e.g. [4, 9, 1, 7, 3, 10, 5, 2, 8, 6]
puts v             # [1, 2, 3, 4, 5, 6, 7, 8, 9, 10] — unchanged

sample(v, n)

Random sample without replacement

Returns n randomly chosen elements. No element is chosen twice.

v = [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]

puts sample(v, 3)   # e.g. [7, 2, 9]
puts sample(v, 1)   # e.g. [4]

n defaults to 1 if omitted:

puts sample(["red", "green", "blue"])   # e.g. ["green"]

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Quick Reference

Function	Description
rand_int(a, b)	Random integer between a and b inclusive
rand_float(a, b)	Random float in [a, b)
rand()	Random float in [0.0, 1.0)
rand(n)	Random integer in [0, n)
rand_seed(n)	Fix seed for reproducibility
shuffle(v)	Return randomly reordered copy of vector
sample(v, n)	Return n randomly chosen elements (no repeats)