Enable depiction of duplicated flows (i.e. two lines with same origin and two different destinations)

[bestekov]

I'll preface by saying I'm not sure whether this is possible in the underlying d3.js library or not. But assuming it is...

Use case: When using a Sankey diagram to depict the flow of data in a system. It is possible for data to be duplicated and flow to two different places.

For example say I have A that sends 1 unit of data to both B and C. If I represent that today like this:

a [1] b
a [1] c

Sankey will produce a view that says the value of A is 2:

However, I would like a way to mark a given set of edges as being a duplication of the flow and therefore overlap. To illustrate I used this input and then manually dragged the lines to overlap:

a1 [1] b
a2 [1] c