## no-std iter_num_tools

Create simple iterators over non integer ranges. itertools + num = iter_num_tools

### 29 releases

 0.7.1 Apr 21, 2023 Apr 21, 2023 Nov 28, 2021 Jun 18, 2021 Dec 26, 2020

#96 in Math

47KB
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# iter-num-tools

This is a collection if iterator extensions that make heavy use of number properties. Mostly extending on Range.

## LinSpace

LinSpace is an iterator over a range with a fixed number of values all evenly spaced.

``````use iter_num_tools::lin_space;

// Count from 1.0 up to and including 5.0, with 5 numbers counted in total
let it = lin_space(1.0..=5.0, 5);
assert!(it.eq([1.0, 2.0, 3.0, 4.0, 5.0]));

// Count from 0.0 up to and excluding 5.0, with 5 numbers counted in total
let it = lin_space(0.0..5.0, 5);
assert!(it.eq([0.0, 1.0, 2.0, 3.0, 4.0]));
``````

## GridSpace

GridSpace extends on LinSpace.

``````use iter_num_tools::grid_space;

// count in 2 dimensions (excluding end points),
// from 0.0 up to 1.0 in the x direction with 2 even steps,
// and 0.0 up to 2.0 in the y direction with 4 even steps
let it = grid_space([0.0, 0.0]..[1.0, 2.0], [2, 4]);
assert!(it.eq([
[0.0, 0.0], [0.5, 0.0],
[0.0, 0.5], [0.5, 0.5],
[0.0, 1.0], [0.5, 1.0],
[0.0, 1.5], [0.5, 1.5],
]));

// count in 2 dimensions (including end points),
// from 0.0 up to 1.0 in the x direction,
// and 0.0 up to 2.0 in the y direction with 3 even steps in all directions
let it = grid_space([0.0, 0.0]..=[1.0, 2.0], 3);
assert!(it.eq([
[0.0, 0.0], [0.5, 0.0], [1.0, 0.0],
[0.0, 1.0], [0.5, 1.0], [1.0, 1.0],
[0.0, 2.0], [0.5, 2.0], [1.0, 2.0],
]));
``````

## Arange

Arange is similar to LinSpace, but instead of a fixed amount of steps, it steps by a fixed amount.

``````use iter_num_tools::arange;

let it = arange(0.0..2.0, 0.5);
assert!(it.eq([0.0, 0.5, 1.0, 1.5]));
``````

#### Note

There is no inclusive version of arange. Consider the following

``````use iter_num_tools::arange;

let it = arange(0.0..=2.1, 0.5);
``````

We would not expect 2.1 to ever be a value that the iterator will ever meet, but the range suggests it should be included. Therefore, no RangeInclusive implementation is provided.

## ArangeGrid

ArangeGrid is the same as GridSpace but for Arange instead of LinSpace.

``````use iter_num_tools::arange_grid;

// count in 2 dimensions,
// from 0.0 up to 1.0 in the x direction,
// and 0.0 up to 2.0 in the y direction,
// stepping by 0.5 each time
let it = arange_grid([0.0, 0.0]..[1.0, 2.0], 0.5);
assert!(it.eq([
[0.0, 0.0], [0.5, 0.0],
[0.0, 0.5], [0.5, 0.5],
[0.0, 1.0], [0.5, 1.0],
[0.0, 1.5], [0.5, 1.5],
]));

// count in 2 dimensions,
// from 0.0 up to 1.0 in the x direction stepping by 0.5 each time,
// and 0.0 up to 2.0 in the y direction stepping by 1.0 each time
let it = arange_grid([0.0, 0.0]..[1.0, 2.0], [0.5, 1.0]);
assert!(it.eq([
[0.0, 0.0], [0.5, 0.0],
[0.0, 1.0], [0.5, 1.0],
]));
``````

## LogSpace

LogSpace is similar to LinSpace, but instead of evenly spaced linear steps, it has evenly spaced logarithmic steps.

``````use iter_num_tools::log_space;
use itertools::zip_eq;

// From 1.0 up to and including 1000.0, taking 4 logarithmic steps
let it = log_space(1.0..=1000.0, 4);
let expected: [f64; 4] = [1.0, 10.0, 100.0, 1000.0];

assert!(zip_eq(it, expected).all(|(x, y)| (x-y).abs() < 1e-10));

// From 1.0 up to 1000.0, taking 3 logarithmic steps
let it = log_space(1.0..1000.0, 3);
let expected: [f64; 3] = [1.0, 10.0, 100.0];

assert!(zip_eq(it, expected).all(|(x, y)| (x-y).abs() < 1e-10));
``````

## Alternatives

There is already a project called `itertools-num` which has quite a few downloads but it isn't optimised for speed or flexibility.

(try this benchmark for yourself: clone the repo and run `cargo bench --bench "linspace" --all-features`)

``````LinSpace/linspace [1.0, 3.0] x100 (iter-num-tools)
time:   [65.311 ns 65.579 ns 65.898 ns]
LinSpace/linspace [1.0, 3.0] x100 (std)
time:   [67.545 ns 67.762 ns 68.047 ns]
LinSpace/linspace [1.0, 3.0] x100 (itertools-num)
time:   [117.05 ns 117.59 ns 118.23 ns]
``````
``````fn bench(i: impl Iterator<Item=f64>) -> Vec<f64> {
black_box(i.map(|x| x * 2.0).collect())
}

// first benchmark (fastest)
bench(iter_num_tools::lin_space(1.0..=3.0, 100));

// second benchmark
fn lin_space_std(start: f64, end: f64, steps: usize) -> impl Iterator<Item = f64> {
let len = end - start;
let step = len / steps as f64;
(0..=steps).map(move |i| start + i as f64 * step)
}
bench(lin_space_std(1.0, 3.0, 100));

// third benchmark (slowest)
bench(itertools_num::linspace(1.0, 3.0, 100));
``````

It also does not provide any other utilities. Only `linspace` (inclusive) and a 'Cumulative sum' iterator adaptor.

~580KB
~12K SLoC