Add ability to sort nodes and edges

[treardon17]

Some of the default layouts in cytoscape have a sort option (or some variation of it) that lets you sort the nodes/edges so the resulting graph is predictable if you're adding/removing nodes.

examples layouts with sort: https://js.cytoscape.org/#layouts/grid https://js.cytoscape.org/#layouts/circle https://js.cytoscape.org/#layouts/breadthfirst

Without this, the graph will have a different outcome if several nodes/edges are added, then some middle nodes/edges are removed, and then those same removed nodes/edges are added back.

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[maxkfranz]

Does Dagre have guarantees, i.e. explicit API documentation, that the ordering of the elements affects the end result?

[treardon17]

@maxkfranz dagre itself doesn't have explicit documentation, but dagre uses graphlib, and graphlib has documentation for the order of nodes: https://github.com/dagrejs/graphlib/wiki/API-Reference#graph-concepts.

From the graphlib docs:

directed: set to true to get a directed graph and false to get an undirected graph. An undirected graph does not treat the order of nodes in an edge as significant. In other words, g.edge("a", "b") === g.edge("b", "a") for an undirected graph. Default: true.

cytoscape dagre uses the default value for directed here, so the order of the nodes are significant.

[maxkfranz]

Great.

What could we do to clarify how this proposed sorting feature would affect the resultant layout, especially for people who are reading the documentation for the first time? The circle layout and grid layout have conventional orderings, clockwise and the Western reading direction respectively (also the typical x/y graphics axes in CS). The natural ordering of a tree is the topology, so the reader can't necessarily make a connection for what sorting would do.

[treardon17]

We could clarify in the docs that by default cycoscape dagre creates a directed graph, and directed graphs use the node order as a tie breaker when defining the topology of a graph. This feature is most useful when adding and removing the same nodes and edges multiple times in a graph.

Would that make sense?

[maxkfranz]

Sounds good

On Sep 21, 2022, at 22:47, Tyler @.***> wrote:

We could clarify in the docs that by default cycoscape dagre creates a directed graph, and directed graphs use the node order as a tie breaker when defining the topology of a graph. This feature is most useful when adding and removing the same nodes and edges multiple times in a graph.

Would that make sense?

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[treardon17]

@maxkfranz I updated the readme based on what we talked about 👍

[maxkfranz]

Great, @treardon17. I'll set aside some time tomorrow for a merge & release

[maxkfranz]

Sorry, this slipped past me somehow.

Released to npm with your updates for 2.5.0

[treardon17]

Thanks @maxkfranz!