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@ -1,39 +0,0 @@
name: Rust
on:
push:
branches: [ "main" ]
pull_request:
branches: [ "main" ]
env:
CARGO_TERM_COLOR: always
jobs:
build:
runs-on: ubuntu-latest
steps:
- uses: actions/checkout@v3
- name: Set up Python 3.11
uses: actions/setup-python@v2
with:
python-version: 3.11
- name: Install dependencies
run: |
python -m pip install --upgrade pip
python -m venv venv
source venv/bin/activate
pip install -r requirements.txt
- name: Build
run: |
source venv/bin/activate
maturin build --verbose
- name: Run tests
run: cargo test --verbose
- name: Run E2E tests
run: |
source venv/bin/activate
maturin develop --release
pytest

3
.gitignore vendored
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@ -1,5 +1,4 @@
/target
result/
venv/
*/__pycache__/
venv/

2
Cargo.lock generated
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@ -33,7 +33,7 @@ dependencies = [
[[package]]
name = "graph_force"
version = "0.2.2"
version = "0.1.0"
dependencies = [
"pyo3",
"rand",

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@ -1,6 +1,6 @@
[package]
name = "graph_force"
version = "0.2.2"
version = "0.1.0"
edition = "2021"
# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html

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@ -1,13 +0,0 @@
## Development
### Setup
```
python3 -m venv venv
source venv/bin/activate
pip install -r requirements.txt
```
### Build
```
maturin develop
```

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@ -2,88 +2,24 @@
A python/rust library for embedding graphs in 2D space, using force-directed layouts.
## Installation
## Development
```bash
pip install graph_force
### Setup
```
python3 -m venv venv
source venv/bin/activate
pip install -r requirements.txt
```
### Build
```
maturin develop
```
## Usage
The first parameter defines the number of nodes in graph.
The second parameter is an iterable of edges, where each edge is a tuple of two integers representing the nodes it connects. Node ids start at 0.
```python
import graph_force
edges = [(0, 1), (1, 2), (2, 3), (3, 0)]
pos = graph_force.layout_from_edge_list(4, edges)
```
### Example with networkx
This library does not have a function to consume a networkx graph directly, but it is easy to convert it to an edge list.
```python
import networkx as nx
import graph_force
G = nx.grid_2d_graph(10, 10)
# we have to map the names to integers
# as graph_force only supports integers as node ids at the moment
edges = []
mapping = {n: i for i, n in enumerate(G.nodes)}
i = 0
for edge in G.edges:
edges.append((mapping[edge[0]], mapping[edge[1]]))
pos = graph_force.layout_from_edge_list(len(G.nodes), edges, iter=1000)
nx.draw(G, {n: pos[i] for n, i in mapping.items()}, node_size=2, width=0.1)
```
### Example with edge file
This methods can be used with large graphs, where the edge list does not fit into memory.
Format of the file:
- Little endian
- 4 bytes: number of nodes(int)
- 12 bytes: nodeA(int), nodeB(int), weight(float)
```python
import graph_force
import struct
with open("edges.bin", "rb") as f:
n = 10
f.write(struct.pack("i", n))
for x in range(n-1):
f.write(struct.pack("iif", x, x+1, 1))
pos = graph_force.layout_from_edge_file("edges.bin", iter=50)
```
### Options
`iter`, `threads` and `model`, `initial_pos` are optional parameters, supported by `layout_from_edge_list` and `layout_from_edge_file`.
```python
pos = graph_force.layout_from_edge_list(
number_of_nodes,
edges,
iter=500, # number of iterations, default 500
threads=0, # number of threads, default 0 (all available)
model="spring_model", # model to use, default "spring_model", other option is "networkx_model"
initial_pos=[(0.4, 0.7), (0.7, 0.2), ...], # initial positions, default None (random)
)
```
#### Available models
- `spring_model`: A simple spring model (my own implementation)
- `networkx_model`: Reimplementation of the [spring model from networkx](https://networkx.org/documentation/stable/reference/generated/networkx.drawing.layout.spring_layout.html)
## Contributing
- [Development](DEVELOPMENT.md)
```

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@ -4,21 +4,11 @@ build-backend = "maturin"
[project]
name = "graph_force"
description = "A library for embedding graphs in 2D space, using force-directed layouts."
keywords = ["graph", "layout", "force-directed"]
authors = [ { email = "niko@rerere.org", name = "Niko Abeler" } ]
maintainers = [ { email = "niko@rerere.org", name = "Niko Abeler" } ]
readme = "README.md"
requires-python = ">=3.11"
requires-python = ">=3.7"
classifiers = [
"Programming Language :: Rust",
"Programming Language :: Python :: Implementation :: CPython",
"Programming Language :: Python :: Implementation :: PyPy",
"Topic :: Scientific/Engineering :: Visualization",
"License :: OSI Approved :: MIT License",
]
[project.urls]
homepage = "https://github.com/H4kor/graph-force/"
repository = "https://github.com/H4kor/graph-force/"

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@ -1,2 +1 @@
maturin==0.14.1
pytest==7.2.0

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@ -34,46 +34,3 @@ pub fn new_node_vector(size: usize) -> NodeVector {
}
Arc::new(nodes)
}
pub fn add_edge(matrix: &mut EdgeMatrix, i: usize, j: usize) {
let mut edges = matrix.write().unwrap();
edges[i][j].weight = 1.0;
edges[j][i].weight = 1.0;
}
#[cfg(test)]
mod test {
use super::*;
#[test]
fn test_new_edge_matrix() {
let matrix = new_edge_matrix(5);
let edges = matrix.read().unwrap();
assert_eq!(edges.len(), 5);
for row in edges.iter() {
assert_eq!(row.len(), 5);
for edge in row.iter() {
assert_eq!(edge.weight, 0.0);
}
}
}
#[test]
fn test_new_node_vector() {
let nodes = new_node_vector(5);
assert_eq!(nodes.len(), 5);
}
#[test]
fn test_add_edge() {
let mut matrix = new_edge_matrix(5);
add_edge(&mut matrix, 0, 1);
let edges = matrix.read().unwrap();
assert_eq!(edges[0][1].weight, 1.0);
assert_eq!(edges[1][0].weight, 1.0);
assert_eq!(edges[0][0].weight, 0.0);
assert_eq!(edges[1][1].weight, 0.0);
}
}

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@ -1,125 +1,25 @@
mod graph;
mod model;
mod networkx_model;
mod reader;
mod runner;
mod spring_model;
mod utils;
use graph::NodeVector;
use pyo3::exceptions;
use pyo3::{prelude::*, types::PyIterator};
use pyo3::prelude::*;
fn pick_model(model: &str) -> Result<Box<dyn model::ForceModel + Send + Sync>, PyErr> {
match model {
"spring_model" => Ok(Box::new(spring_model::SimpleSpringModel::new(1.0))),
"networkx_model" => Ok(Box::new(networkx_model::NetworkXModel::new())),
_ => {
return Err(PyErr::new::<exceptions::PyValueError, _>(
"model must be either 'spring_model' or 'networkx_model'",
))
}
}
}
fn initial_pos_to_node_vector(initial_pos: Option<Vec<(f32, f32)>>) -> Option<NodeVector> {
match initial_pos {
Some(pos) => {
let nodes = graph::new_node_vector(pos.len());
for (i, (x, y)) in pos.iter().enumerate() {
let mut node = nodes[i].write().unwrap();
node.x = *x;
node.y = *y;
}
Some(nodes)
}
None => None,
}
}
#[pyfunction(
file_path,
"*",
iter = 500,
threads = 0,
model = "\"spring_model\"",
initial_pos = "None"
)]
fn layout_from_edge_file(
file_path: &str,
iter: usize,
threads: usize,
model: &str,
initial_pos: Option<Vec<(f32, f32)>>,
) -> PyResult<Vec<(f32, f32)>> {
let (size, matrix) = reader::read_graph(file_path);
let model = pick_model(model)?;
let r = runner::Runner::new(iter, threads);
Ok(r.layout(size, matrix, model, initial_pos_to_node_vector(initial_pos)))
}
#[pyfunction(
number_of_nodes,
edges,
"*",
iter = 500,
threads = 0,
model = "\"spring_model\"",
initial_pos = "None"
)]
/// Formats the sum of two numbers as string.
#[pyfunction(number_of_nodes, edges, "*", iter = 500, threads = 0)]
fn layout_from_edge_list(
number_of_nodes: usize,
edges: &PyAny,
edges: Vec<(u32, u32)>,
iter: usize,
threads: usize,
model: &str,
initial_pos: Option<Vec<(f32, f32)>>,
) -> PyResult<Vec<(f32, f32)>> {
let model: Box<dyn model::ForceModel + Send + Sync> = pick_model(model)?;
let mut edge_matrix = graph::new_edge_matrix(number_of_nodes);
match edges.extract::<&PyIterator>() {
Ok(iter) => {
iter.iter()?
.map(|edge| edge.and_then(PyAny::extract::<(usize, usize)>))
.for_each(|edge| {
if let Ok((u, v)) = edge {
graph::add_edge(&mut edge_matrix, u, v);
}
});
for edge in iter {
let edge = edge?;
let edge = edge.extract::<(usize, usize)>()?;
graph::add_edge(&mut edge_matrix, edge.0, edge.1);
}
}
Err(_) => match edges.extract::<Vec<(usize, usize)>>() {
Ok(edge) => {
for edge in edge {
graph::add_edge(&mut edge_matrix, edge.0, edge.1);
}
}
Err(_) => {
return Err(PyErr::new::<exceptions::PyTypeError, _>(
"Edges must be an iterable of (int, int)",
));
}
},
}
let r = runner::Runner::new(iter, threads);
Ok(r.layout(
number_of_nodes,
edge_matrix,
model,
initial_pos_to_node_vector(initial_pos),
))
Ok(r.layout(number_of_nodes, edges))
}
/// A Python module implemented in Rust.
#[pymodule]
fn graph_force(_py: Python, m: &PyModule) -> PyResult<()> {
m.add_function(wrap_pyfunction!(layout_from_edge_list, m)?)?;
m.add_function(wrap_pyfunction!(layout_from_edge_file, m)?)?;
Ok(())
}

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@ -1,7 +0,0 @@
use crate::graph::{EdgeMatrix, Node, NodeVector};
pub trait ForceModel {
fn init(&mut self, edges: EdgeMatrix, size: usize, iterations: usize);
fn prepare(&mut self, _nodes: &NodeVector);
fn step(&self, nodes: &NodeVector, i_node: usize) -> Node;
}

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@ -1,133 +0,0 @@
use crate::graph::{new_edge_matrix, EdgeMatrix, Node, NodeVector};
use crate::model::ForceModel;
/**
* Translation of the NetworkX spring_layout function.
* https://networkx.org/documentation/stable/reference/generated/networkx.drawing.layout.spring_layout.html
*/
pub struct NetworkXModel {
edges: EdgeMatrix,
size: usize,
k: f32, // optimal distance
t: f32, // temperature
dt: f32, // temperature decrease
}
impl NetworkXModel {
pub fn new() -> Self {
NetworkXModel {
edges: new_edge_matrix(0),
size: 0,
k: 1.0,
t: 1.0,
dt: 0.0,
}
}
}
impl ForceModel for NetworkXModel {
fn init(&mut self, edges: EdgeMatrix, size: usize, iterations: usize) {
self.k = (1.0 / size as f32).sqrt();
self.t = 0.1;
self.dt = self.t / ((iterations + 1) as f32);
self.t += self.dt; // prepare is called before the first step
self.edges = edges;
self.size = size;
}
fn prepare(&mut self, _nodes: &NodeVector) {
self.t -= self.dt; // decrease temperature
}
fn step(&self, nodes: &NodeVector, i_node: usize) -> Node {
let node = nodes[i_node].read().unwrap();
let edges = self.edges.read().unwrap();
let node_x = node.x;
let node_y = node.y;
let mut displacement_x = 0.0;
let mut displacement_y = 0.0;
for o in 0..self.size {
if o == i_node {
continue;
}
let edge = edges[i_node][o].weight;
let o_x: f32;
let o_y: f32;
{
let other = nodes[o].read().unwrap();
o_x = other.x;
o_y = other.y;
}
// difference between node and other
let delta_x = node_x - o_x;
let delta_y = node_y - o_y;
// distance between node and other
let dist = (delta_x * delta_x + delta_y * delta_y).sqrt();
// enforce minimum distance of 0.01
let dist = if dist < 0.01 { 0.01 } else { dist };
// displacement "force"
displacement_x += delta_x * (self.k.powi(2) / dist.powi(2) - edge * dist / self.k);
displacement_y += delta_y * (self.k.powi(2) / dist.powi(2) - edge * dist / self.k);
}
// update positions
let length = (displacement_x * displacement_x + displacement_y * displacement_y).sqrt();
let length = if length < 0.01 { 0.01 } else { length };
let delta_pos_x = displacement_x * self.t / length;
let delta_pos_y = displacement_y * self.t / length;
Node {
x: node_x + delta_pos_x,
y: node_y + delta_pos_y,
}
}
}
#[cfg(test)]
mod test {
use super::*;
use crate::graph::{new_edge_matrix, new_node_vector};
#[test]
fn test_simple_spring_model_attraction() {
let mut model = NetworkXModel::new();
let edges = new_edge_matrix(2);
edges.write().unwrap()[0][1].weight = 1.0;
edges.write().unwrap()[1][0].weight = 1.0;
model.init(edges, 2, 1);
let nodes = new_node_vector(2);
nodes[0].write().unwrap().x = 0.0;
nodes[0].write().unwrap().y = 0.0;
nodes[1].write().unwrap().x = 1.0;
nodes[1].write().unwrap().y = 1.0;
model.prepare(&nodes);
let node = model.step(&nodes, 0);
assert!(node.x > 0.0);
assert!(node.y > 0.0);
}
#[test]
fn test_simple_spring_model_repulsion() {
let mut model = NetworkXModel::new();
let edges = new_edge_matrix(2);
model.init(edges, 2, 1);
let nodes = new_node_vector(2);
nodes[0].write().unwrap().x = 0.0;
nodes[0].write().unwrap().y = 0.0;
nodes[1].write().unwrap().x = 1.0;
nodes[1].write().unwrap().y = 1.0;
model.prepare(&nodes);
let node = model.step(&nodes, 0);
assert!(node.x < 0.0);
assert!(node.y < 0.0);
}
}

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@ -1,7 +1,3 @@
use std::{fs::File, io::Read};
use crate::graph::{add_edge, new_edge_matrix, EdgeMatrix};
/**
* Read Graph data from file
* Format:
@ -9,20 +5,22 @@ use crate::graph::{add_edge, new_edge_matrix, EdgeMatrix};
* - 4 bytes: number of nodes(int)
* - 12 bytes: nodeA(int), nodeB(int), weight(float)
*/
pub fn read_graph(file_name: &str) -> (usize, EdgeMatrix) {
fn read_graph(file_name: &str) -> (usize, EdgeMatrix) {
let mut file = File::open(file_name).expect("file not found");
let mut size_buffer = [0; 4];
file.read_exact(&mut size_buffer).expect("buffer overflow");
let size = u32::from_le_bytes(size_buffer) as usize;
let mut matrix = new_edge_matrix(size);
let matrix_ptr = connection_matrix(size);
{
let mut matrix = matrix_ptr.write().unwrap();
let mut buffer = [0; 12];
while file.read_exact(&mut buffer).is_ok() {
let node_a = u32::from_le_bytes(buffer[0..4].try_into().unwrap()) as usize;
let node_b = u32::from_le_bytes(buffer[4..8].try_into().unwrap()) as usize;
let _weight = f32::from_le_bytes(buffer[8..12].try_into().unwrap());
add_edge(&mut matrix, node_a, node_b);
let weight = f32::from_le_bytes(buffer[8..12].try_into().unwrap());
matrix[node_a][node_b].weight = weight;
matrix[node_b][node_a].weight = weight;
}
}
(size, matrix)
(size, matrix_ptr)
}

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@ -1,5 +1,5 @@
use crate::graph::{new_node_vector, EdgeMatrix, NodeVector};
use crate::model::ForceModel;
use crate::graph::{new_edge_matrix, new_node_vector, EdgeMatrix};
use crate::spring_model;
use crate::utils;
use std::sync::{Arc, RwLock};
use std::thread;
@ -33,23 +33,19 @@ impl Runner {
pub fn layout(
self: &Self,
number_of_nodes: usize,
edges: EdgeMatrix,
model: Box<dyn ForceModel + Send + Sync>,
initial_pos: Option<NodeVector>,
edge_list: Vec<(u32, u32)>,
) -> Vec<(f32, f32)> {
// let edges = connection_matrix(size);
let mut nodes = match initial_pos {
Some(pos) => pos,
None => new_node_vector(number_of_nodes),
};
let edges = edge_matrix_from_edge_list(number_of_nodes, edge_list);
let mut nodes = new_node_vector(number_of_nodes);
let mut nodes_next = new_node_vector(number_of_nodes);
let model = Arc::new(RwLock::new(model));
model
.write()
.unwrap()
.init(edges, number_of_nodes, self.iterations);
// let model = Arc::new(RwLock::new(spring_model::InitialModel::new(edges, number_of_nodes)));
let model = Arc::new(RwLock::new(spring_model::MyModel::new(
edges,
number_of_nodes,
self.iterations,
)));
let chunks = utils::gen_chunks(number_of_nodes, self.threads);
for _epoch in 0..self.iterations {
@ -90,35 +86,14 @@ impl Runner {
}
}
#[cfg(test)]
mod test {
use crate::graph::{self, Node, NodeVector};
use super::*;
struct MockModel {
counter: usize,
}
impl ForceModel for MockModel {
fn init(&mut self, _edges: EdgeMatrix, _size: usize, _iterations: usize) {}
fn prepare(&mut self, _nodes: &NodeVector) {
self.counter += 1;
}
fn step(&self, _nodes: &NodeVector, i_node: usize) -> Node {
Node {
x: i_node as f32,
y: self.counter as f32,
}
fn edge_matrix_from_edge_list(number_of_nodes: usize, edge_list: Vec<(u32, u32)>) -> EdgeMatrix {
let matrix_ptr = new_edge_matrix(number_of_nodes as usize);
{
let mut matrix = matrix_ptr.write().unwrap();
for (node_a, node_b) in edge_list {
matrix[node_a as usize][node_b as usize].weight = 1.0;
matrix[node_b as usize][node_a as usize].weight = 1.0;
}
}
#[test]
fn test_layout() {
let model = Box::new(MockModel { counter: 0 });
let runner = Runner::new(10, 1);
let edges = graph::new_edge_matrix(3);
let result = runner.layout(3, edges, model, None);
assert_eq!(result, vec![(0.0, 10.0), (1.0, 10.0), (2.0, 10.0)]);
}
matrix_ptr
}

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@ -1,37 +1,32 @@
use crate::graph::{new_edge_matrix, EdgeMatrix, Node, NodeVector};
use crate::model::ForceModel;
pub struct SimpleSpringModel {
use crate::graph::{EdgeMatrix, Node, NodeVector};
pub struct MyModel {
edges: EdgeMatrix,
size: usize,
opt_dist: f32,
c: f32,
dc: f32,
}
impl SimpleSpringModel {
pub fn new(c: f32) -> Self {
SimpleSpringModel {
edges: new_edge_matrix(0),
size: 0,
c,
dc: 0.0,
impl MyModel {
pub fn new(edges: EdgeMatrix, size: usize, iterations: usize) -> MyModel {
let opt_dist = 1.0;
let c = 0.1;
MyModel {
edges,
size,
opt_dist,
c: c,
dc: c / ((iterations + 1) as f32),
}
}
}
impl ForceModel for SimpleSpringModel {
fn init(&mut self, edges: EdgeMatrix, size: usize, iterations: usize) {
let dc = self.c / ((iterations + 1) as f32);
self.edges = edges;
self.size = size;
self.dc = dc;
}
fn prepare(&mut self, _nodes: &NodeVector) {
pub fn prepare(&mut self, _nodes: &NodeVector) {
self.c -= self.dc;
}
fn step(&self, nodes: &NodeVector, i_node: usize) -> Node {
pub fn step(&self, nodes: &NodeVector, i_node: usize) -> Node {
let node = nodes[i_node].read().unwrap();
let edges = self.edges.read().unwrap();
@ -62,14 +57,14 @@ impl ForceModel for SimpleSpringModel {
let edge = edges[i_node][o].weight;
if edge == 0.0 {
let f_rep = dist.powi(2).recip().min(1.0);
let f_rep = dist.powi(2).recip().min(self.opt_dist);
let f_rep_x = f_rep * unit_x;
let f_rep_y = f_rep * unit_y;
sum_x -= f_rep_x;
sum_y -= f_rep_y;
} else {
let f_spring = 0.5 * (dist - 1.0);
let f_spring = 0.5 * (dist - self.opt_dist);
let f_spring_x = f_spring * unit_x;
let f_spring_y = f_spring * unit_y;
sum_x += f_spring_x;
@ -89,47 +84,3 @@ impl ForceModel for SimpleSpringModel {
}
}
}
#[cfg(test)]
mod test {
use super::*;
use crate::graph::{new_edge_matrix, new_node_vector};
#[test]
fn test_simple_spring_model_attraction() {
let mut model = SimpleSpringModel::new(1.0);
let edges = new_edge_matrix(2);
edges.write().unwrap()[0][1].weight = 1.0;
edges.write().unwrap()[1][0].weight = 1.0;
model.init(edges, 2, 1);
let nodes = new_node_vector(2);
nodes[0].write().unwrap().x = 0.0;
nodes[0].write().unwrap().y = 0.0;
nodes[1].write().unwrap().x = 1.0;
nodes[1].write().unwrap().y = 1.0;
model.prepare(&nodes);
let node = model.step(&nodes, 0);
assert!(node.x > 0.0);
assert!(node.y > 0.0);
}
#[test]
fn test_simple_spring_model_repulsion() {
let mut model = SimpleSpringModel::new(1.0);
let edges = new_edge_matrix(2);
model.init(edges, 2, 1);
let nodes = new_node_vector(2);
nodes[0].write().unwrap().x = 0.0;
nodes[0].write().unwrap().y = 0.0;
nodes[1].write().unwrap().x = 1.0;
nodes[1].write().unwrap().y = 1.0;
model.prepare(&nodes);
let node = model.step(&nodes, 0);
assert!(node.x < 0.0);
assert!(node.y < 0.0);
}
}

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@ -3,18 +3,11 @@ use std::ops::Range;
pub fn gen_chunks(n: usize, chunks: usize) -> Vec<Range<usize>> {
let mut borders = vec![];
let chunk_size = n / chunks;
let mut remainder = n % chunks;
let mut start = 0;
for _ in 0..chunks {
let end = start + chunk_size;
if remainder > 0 {
remainder -= 1;
borders.push(start..end + 1);
start = end + 1;
} else {
borders.push(start..end);
start = end;
}
borders.push(start..end);
start = end;
}
// Change the last chunk to include the remainder
let size = borders.len();
@ -29,7 +22,7 @@ mod test {
#[test]
fn test_gen_chunks() {
let borders = gen_chunks(10, 3);
assert_eq!(borders, vec![(0..4), (4..7), (7..10)]);
assert_eq!(borders, vec![(0..3), (3..6), (6..10)]);
}
#[test]
@ -43,10 +36,4 @@ mod test {
let borders = gen_chunks(10, 1);
assert_eq!(borders, vec![(0..10)]);
}
#[test]
fn test_gen_chunks4() {
let borders = gen_chunks(11, 3);
assert_eq!(borders, vec![(0..4), (4..8), (8..11)]);
}
}

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@ -1,50 +0,0 @@
import graph_force
import struct
def test_list_of_edges():
edges = [(1, 2), (2, 3), (3, 4), (4, 5), (5, 6)]
pos = graph_force.layout_from_edge_list(7, edges)
assert pos is not None
assert len(pos) == 7
def test_iterator_of_edges():
pos = graph_force.layout_from_edge_list(
7,
((0, i + 1) for i in range(6))
)
assert pos is not None
assert len(pos) == 7
def test_tuple_of_edges():
pos = graph_force.layout_from_edge_list(
7,
((0,1), (1,2), (2,3), (3,4), (4,5), (5,6))
)
assert pos is not None
assert len(pos) == 7
def test_model_selection():
edges = [(1, 2), (2, 3), (3, 4), (4, 5), (5, 6)]
pos = graph_force.layout_from_edge_list(7, edges, model='networkx_model')
assert pos is not None
assert len(pos) == 7
def test_from_file():
with open("/tmp/edges.bin", "wb") as f:
n = 10
f.write(struct.pack("i", n))
for x in range(n-1):
f.write(struct.pack("iif", x, x+1, 1))
pos = graph_force.layout_from_edge_file('/tmp/edges.bin')
assert pos is not None
assert len(pos) == 10
def test_initial_pos():
edges = [(1, 2), (2, 3), (3, 4), (4, 5), (5, 6)]
initial = [(i, i) for i in range(7)]
pos = graph_force.layout_from_edge_list(7, edges, iter=0, initial_pos=initial)
assert pos is not None
assert len(pos) == 7
assert pos == initial