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

## Installing

If you use NPM, `npm install d3-chord`

. Otherwise, download the latest release. You can also load directly from d3js.org, either as a standalone library or as part of D3 4.0. AMD, CommonJS, and vanilla environments are supported. In vanilla, a `d3`

global is exported:

```
<script src="https://d3js.org/d3-array.v1.min.js"></script>
<script src="https://d3js.org/d3-path.v1.min.js"></script>
<script src="https://d3js.org/d3-chord.v1.min.js"></script>
<script>
var chord = d3.chord();
</script>
```

## API Reference

Constructs a new chord layout with the default settings.

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 *i*th node in the network to the *j*th 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:

```
var 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*`subindex`

- the node index*j*

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*]. In other words, *chord*.source.index equals *chord*.target.subindex, *chord*.source.subindex equals *chord*.target.index, *chord*.source.value is greater than or equal to *chord*.target.value, and *chord*.source.value is always greater than zero.

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.

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*]) <>

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*]) <>

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*]) <>

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.

Creates a new ribbon generator with the default settings.

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:

```
var 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:

```
var 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.

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;
}
```

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;
}
```

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

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

# *ribbon*.**startAngle**([*angle*]) <>

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.

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*.**context**([*context*]) <>

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.