D3: force layout should have option to set random number generator seed

[ghost]

Because the force layout uses Math.random() to generate random numbers, the layout looks different every time a page is reloaded. It would be useful to add the option to set a random number seed so that there is an option of reproducible layouts.

[mbostock]

Unfortunately, JavaScript doesn't have a seeded random number generator, and I don't really want to implement one from scratch. Also, due to floating point error and interaction (hover-on-fixed, dragging), even a seeded random number generator would not guarantee deterministic output.

If you want to guarantee a particular layout, I run the force layout locally and then save the _x_ and _y_ coordinates it produces to a file. Then initialize your nodes with these pre-computed coordinates, and the layout will stay in the same position. You can see an example of this technique in the interactive At the National Conventions, the Words They Used.

[cmap]

Could we use http://davidbau.com/archives/2010/01/30/random_seeds_coded_hints_and_quintillions.html instead of Math.random? Unfortunately your workaround doesn't for my particular use case.

[mikeazo]

@cmap I know this is old, but thought I'd share something I found. https://github.com/davidbau/seedrandom seems to work pretty well for making the force layout more or less deterministic. Here is a JSFiddle I adapted: http://jsfiddle.net/s8pcecka/2/

Unfortunately, it isn't completely cross-browser. Chrome and Firefox resulted in very similar layouts. Safari was fairly different. Haven't done much IE testing.

[coli]

Wow that is incredible, thanks for sharing.