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Basics: improve random number examples

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Diggory Hardy 2017-07-22 15:13:29 +01:00 committed by Brian Anderson
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src/basics.md
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@ -4,7 +4,7 @@
|--------|--------|------------|
| [Read lines of strings from a file][ex-std-read-lines] | [![std-badge]][std] | [![cat-filesystem-badge]][cat-filesystem] |
| [Read and write integers in little-endian byte order][ex-byteorder-le] | [![byteorder-badge]][byteorder] | [![cat-encoding-badge]][cat-encoding] |
| [Generate random floating point numbers][ex-rand-float] | [![rand-badge]][rand] | [![cat-science-badge]][cat-science] |
| [Generate random numbers for simple types][ex-rand-simple] | [![rand-badge]][rand] | [![cat-science-badge]][cat-science] |
| [Generate random numbers within a range][ex-rand-range] | [![rand-badge]][rand] | [![cat-science-badge]][cat-science] |
| [Generate random numbers with normal distribution][ex-rand-dist] | [![rand-badge]][rand] | [![cat-science-badge]][cat-science] |
| [Generate random values of a custom type][ex-rand-custom] | [![rand-badge]][rand] | [![cat-science-badge]][cat-science] |
@ -115,9 +115,11 @@ fn decode(mut bytes: &[u8]) -> Result<Payload> {
# quick_main!(run);
```
[ex-rand-float]: #ex-rand-float
<a name="ex-rand-float"></a>
## Generate random floating point numbers
[ex-rand-simple]: #ex-rand-simple
<a name="ex-rand-simple"></a>
## Generate random numbers for simple types
The `rand` crate provides a convenient source of psuedo-random numbers.
[![rand-badge]][rand] [![cat-science-badge]][cat-science]
@ -126,11 +128,30 @@ extern crate rand;
use rand::Rng;
fn main() {
// Each thread has an automatically-initialised random number generator:
let mut rng = rand::thread_rng();
println!("Random f64: {}", rng.gen::<f64>());
// Integers are uniformly distributed over the type's whole range:
let n1: u32 = rng.gen();
let n2: u16 = rng.gen();
let n3: u8 = rng.gen();
println!("Random u32, u16, u8: {}, {}, {}", n1, n2, n3);
println!("Random i32: {}", rng.gen::<i32>());
// Floating point numbers are uniformly distributed in the half-open range [0, 1)
println!("Random float: {}", rng.gen::<f64>());
println!("Random floats: {:?}", (0..5).map(|_| rng.gen()).collect::<Vec<f32>>());
}
```
Example output:
```
Random u32, u16, u8: 1224630198, 31187, 43
Random i32: -515338046
Random float: 0.7258180295601702
Random floats: [0.6633928, 0.4400041, 0.49633145, 0.02997303, 0.41612816]
```
[ex-rand-range]: #ex-rand-range
<a name="ex-rand-range"></a>
## Generate random numbers within a range
@ -146,10 +167,35 @@ use rand::Rng;
fn main() {
let mut rng = rand::thread_rng();
println!("{}", rng.gen_range(0, 10));
println!("Integer: {}", rng.gen_range(0, 10));
println!("Float: {}", rng.gen_range(0.0, 10.0));
}
```
Alternatively, one can use the [`Range`](https://doc.rust-lang.org/rand/rand/distributions/range/struct.Range.html) distribution.
This has the same effect, but may be faster when repeatedly generating numbers
in the same range.
```rust
extern crate rand;
use rand::distributions::{Range, IndependentSample};
fn main() {
let mut rng = rand::thread_rng();
let die = Range::new(1, 7);
loop {
let throw = die.ind_sample(&mut rng);
println!("Roll the die: {}", throw);
if throw == 6 {
break;
}
}
}
```
[ex-rand-dist]: #ex-rand-dist
<a name="ex-rand-dist"></a>
## Generate random numbers with normal distribution