d3-chord

What is d3-chord?

The d3-chord npm package is a part of the D3.js library that provides tools for creating chord diagrams. Chord diagrams are a graphical method of displaying the inter-relationships between data in a matrix format. This package is particularly useful for visualizing complex relationships in a clear and aesthetically pleasing way.

What are d3-chord's main functionalities?

Generate Chord Layout

This feature allows you to generate a chord layout from a given matrix. The code sample demonstrates how to create a chord layout with padding between groups and sorting subgroups in descending order.

const d3 = require('d3-chord');
const matrix = [
  [11975,  5871, 8916, 2868],
  [ 1951, 10048, 2060, 6171],
  [ 8010, 16145, 8090, 8045],
  [ 1013,   990,  940, 6907]
];
const chord = d3.chord().padAngle(0.05).sortSubgroups(d3.descending);
const chords = chord(matrix);
console.log(chords);

Create Ribbon Paths

This feature allows you to create ribbon paths for the chords. The code sample demonstrates how to create a ribbon path with a specified radius.

const d3 = require('d3-chord');
const ribbon = d3.ribbon().radius(200);
const pathData = ribbon({
  source: {startAngle: 0, endAngle: Math.PI / 2, radius: 200},
  target: {startAngle: Math.PI, endAngle: 3 * Math.PI / 2, radius: 200}
});
console.log(pathData);

Customize Chord Diagram

This feature allows you to customize the chord diagram by adjusting the padding angle and sorting the chords. The code sample demonstrates how to create a chord layout with a larger padding angle and sorting the chords in ascending order.

const d3 = require('d3-chord');
const chord = d3.chord().padAngle(0.1).sortChords(d3.ascending);
const matrix = [
  [11975,  5871, 8916, 2868],
  [ 1951, 10048, 2060, 6171],
  [ 8010, 16145, 8090, 8045],
  [ 1013,   990,  940, 6907]
];
const chords = chord(matrix);
console.log(chords);

Other packages similar to d3-chord

d3-sankey

The d3-sankey package is used for creating Sankey diagrams, which are another type of flow diagram that visualizes the flow of data between different nodes. While d3-chord focuses on relationships in a matrix format, d3-sankey is more suited for visualizing the flow of quantities between different stages or categories.

d3-hierarchy

The d3-hierarchy package is used for creating hierarchical layouts such as tree diagrams, cluster diagrams, and treemaps. Unlike d3-chord, which is used for visualizing relationships in a matrix, d3-hierarchy is used for visualizing hierarchical data structures.

d3-force

The d3-force package is used for creating force-directed graphs, which are used to visualize networks of nodes and links. While d3-chord is used for visualizing relationships in a matrix, d3-force is more suited for visualizing network structures where nodes are connected by links.

README

d3-chord

Visualize relationships or network flow with an aesthetically-pleasing circular layout.

Installing

If you use npm, npm install d3-chord. You can also download the latest release on GitHub. For vanilla HTML in modern browsers, import d3-chord from Skypack:

<script type="module">

import {chord} from "https://cdn.skypack.dev/d3-chord@3";

const c = chord();

</script>

For legacy environments, you can load d3-chord’s UMD bundle from an npm-based CDN such as jsDelivr; a d3 global is exported:

<script src="https://cdn.jsdelivr.net/npm/d3-path@3"></script>
<script src="https://cdn.jsdelivr.net/npm/d3-chord@3"></script>
<script>

const chord = d3.chord();

</script>

API Reference

# d3.chord() · Source

Constructs a new chord layout with the default settings.

# chord(matrix) · Source

Computes the chord layout for the specified square matrix of size n×n, where the matrix represents the directed flow amongst a network (a complete digraph) of n nodes. The given matrix must be an array of length n, where each element matrix[i] is an array of n numbers, where each matrix[i][j] represents the flow from the ith node in the network to the jth node. Each number matrix[i][j] must be nonnegative, though it can be zero if there is no flow from node i to node j. From the Circos tableviewer example:

const matrix = [
  [11975,  5871, 8916, 2868],
  [ 1951, 10048, 2060, 6171],
  [ 8010, 16145, 8090, 8045],
  [ 1013,   990,  940, 6907]
];

The return value of chord(matrix) is an array of chords, where each chord represents the combined bidirectional flow between two nodes i and j (where i may be equal to j) and is an object with the following properties:

• source - the source subgroup
• target - the target subgroup

Each source and target subgroup is also an object with the following properties:

• startAngle - the start angle in radians
• endAngle - the end angle in radians
• value - the flow value matrix[i][j]
• index - the node index i

The chords are typically passed to d3.ribbon to display the network relationships. The returned array includes only chord objects for which the value matrix[i][j] or matrix[j][i] is non-zero. Furthermore, the returned array only contains unique chords: a given chord ij represents the bidirectional flow from i to j and from j to i, and does not contain a duplicate chord ji; i and j are chosen such that the chord’s source always represents the larger of matrix[i][j] and matrix[j][i].

The chords array also defines a secondary array of length n, chords.groups, where each group represents the combined outflow for node i, corresponding to the elements matrix[i][0 … n - 1], and is an object with the following properties:

• startAngle - the start angle in radians
• endAngle - the end angle in radians
• value - the total outgoing flow value for node i
• index - the node index i

The groups are typically passed to d3.arc to produce a donut chart around the circumference of the chord layout.

# chord.padAngle([angle]) · Source

If angle is specified, sets the pad angle between adjacent groups to the specified number in radians and returns this chord layout. If angle is not specified, returns the current pad angle, which defaults to zero.

# chord.sortGroups([compare]) · Source

If compare is specified, sets the group comparator to the specified function or null and returns this chord layout. If compare is not specified, returns the current group comparator, which defaults to null. If the group comparator is non-null, it is used to sort the groups by their total outflow. See also d3.ascending and d3.descending.

# chord.sortSubgroups([compare]) · Source

If compare is specified, sets the subgroup comparator to the specified function or null and returns this chord layout. If compare is not specified, returns the current subgroup comparator, which defaults to null. If the subgroup comparator is non-null, it is used to sort the subgroups corresponding to matrix[i][0 … n - 1] for a given group i by their total outflow. See also d3.ascending and d3.descending.

# chord.sortChords([compare]) · Source

If compare is specified, sets the chord comparator to the specified function or null and returns this chord layout. If compare is not specified, returns the current chord comparator, which defaults to null. If the chord comparator is non-null, it is used to sort the chords by their combined flow; this only affects the z-order of the chords. See also d3.ascending and d3.descending.

# d3.chordDirected() · Source, Examples

A chord layout for directional flows. The chord from i to j is generated from the value in matrix[i][j] only.

# d3.chordTranspose() · Source

A transposed chord layout. Useful to highlight outgoing (rather than incoming) flows.

# d3.ribbon() · Source

Creates a new ribbon generator with the default settings.

# ribbon(arguments…) · Source

Generates a ribbon for the given arguments. The arguments are arbitrary; they are simply propagated to the ribbon generator’s accessor functions along with the this object. For example, with the default settings, a chord object expected:

const ribbon = d3.ribbon();

ribbon({
  source: {startAngle: 0.7524114, endAngle: 1.1212972, radius: 240},
  target: {startAngle: 1.8617078, endAngle: 1.9842927, radius: 240}
}); // "M164.0162810494058,-175.21032946354026A240,240,0,0,1,216.1595644740915,-104.28347273835429Q0,0,229.9158815306728,68.8381247563705A240,240,0,0,1,219.77316791012538,96.43523560788266Q0,0,164.0162810494058,-175.21032946354026Z"

Or equivalently if the radius is instead defined as a constant:

const ribbon = d3.ribbon()
    .radius(240);

ribbon({
  source: {startAngle: 0.7524114, endAngle: 1.1212972},
  target: {startAngle: 1.8617078, endAngle: 1.9842927}
}); // "M164.0162810494058,-175.21032946354026A240,240,0,0,1,216.1595644740915,-104.28347273835429Q0,0,229.9158815306728,68.8381247563705A240,240,0,0,1,219.77316791012538,96.43523560788266Q0,0,164.0162810494058,-175.21032946354026Z"

If the ribbon generator has a context, then the ribbon is rendered to this context as a sequence of path method calls and this function returns void. Otherwise, a path data string is returned.

# ribbon.source([source]) · Source

If source is specified, sets the source accessor to the specified function and returns this ribbon generator. If source is not specified, returns the current source accessor, which defaults to:

function source(d) {
  return d.source;
}

# ribbon.target([target]) · Source

If target is specified, sets the target accessor to the specified function and returns this ribbon generator. If target is not specified, returns the current target accessor, which defaults to:

function target(d) {
  return d.target;
}

# ribbon.radius([radius]) · Source

If radius is specified, sets the source and target radius accessor to the specified function and returns this ribbon generator. If radius is not specified, returns the current source radius accessor, which defaults to:

function radius(d) {
  return d.radius;
}

# ribbon.sourceRadius([radius]) · Source

If radius is specified, sets the source radius accessor to the specified function and returns this ribbon generator. If radius is not specified, returns the current source radius accessor, which defaults to:

function radius(d) {
  return d.radius;
}

# ribbon.targetRadius([radius]) · Source

If radius is specified, sets the target radius accessor to the specified function and returns this ribbon generator. If radius is not specified, returns the current target radius accessor, which defaults to:

function radius(d) {
  return d.radius;
}

By convention, the target radius in asymmetric chord diagrams is typically inset from the source radius, resulting in a gap between the end of the directed link and its associated group arc.

# ribbon.startAngle([angle]) · Source

If angle is specified, sets the start angle accessor to the specified function and returns this ribbon generator. If angle is not specified, returns the current start angle accessor, which defaults to:

function startAngle(d) {
  return d.startAngle;
}

The angle is specified in radians, with 0 at -y (12 o’clock) and positive angles proceeding clockwise.

# ribbon.endAngle([angle]) · Source

If angle is specified, sets the end angle accessor to the specified function and returns this ribbon generator. If angle is not specified, returns the current end angle accessor, which defaults to:

function endAngle(d) {
  return d.endAngle;
}

The angle is specified in radians, with 0 at -y (12 o’clock) and positive angles proceeding clockwise.

# ribbon.padAngle([angle]) · Source

If angle is specified, sets the pad angle accessor to the specified function and returns this ribbon generator. If angle is not specified, returns the current pad angle accessor, which defaults to:

function padAngle() {
  return 0;
}

The pad angle specifies the angular gap between adjacent ribbons.

# ribbon.context([context]) · Source

If context is specified, sets the context and returns this ribbon generator. If context is not specified, returns the current context, which defaults to null. If the context is not null, then the generated ribbon is rendered to this context as a sequence of path method calls. Otherwise, a path data string representing the generated ribbon is returned. See also d3-path.

# d3.ribbonArrow() · Source

Creates a new arrow ribbon generator with the default settings.

# ribbonArrow.headRadius([radius]) · Source

If radius is specified, sets the arrowhead radius accessor to the specified function and returns this ribbon generator. If radius is not specified, returns the current arrowhead radius accessor, which defaults to:

function headRadius() {
  return 10;
}