Add embed option exportDataSet to set the data used when opening source/opening in editor

[mcintyre94]

Closes #719

This PR adds a new optional embed option exportDataSet. If it is set, then when the "Open Source" and "Open in Vega Editor" actions are used the data set given is used as the data.values of the spec before it is opened.

This means that it is possible to use Vega's changeset functionality to modify the data, and then open source/editor to eg. extract the latest data or to iterate on the chart in the editor with the latest data available.

I've also added an example file test-changeset.html which demonstrates this feature (and changesets more widely). This is based on the streaming demo: https://vega.github.io/vega-lite/tutorials/streaming.html

Here's a short video showing this working. Note that without this PR the data would be empty in both cases and the editor wouldn't render any data.

vega-embed-export-dataset.mov

[domoritz]

Thanks for the pull request. I think this solution is too brittle as it only works for Vega-Lite.

Instead, we should send the view state via postMessage to the editor.

[mcintyre94]

Instead, we should send the view state via postMessage to the editor.

Thanks for taking a look! Isn't this what the post function that I'm sending the data in is already doing though? It looks like its implementation is opening the editor window and then sending the data with postMessage. Are you saying that it should send the spec unmodified, and then send a secondary message to update it? Or am I updating the wrong thing by updating the spec?

[mcintyre94]

I've just pushed an updated version which does at least work with test-vg.html:

• The data pushed to the editor now has a name as well as the values
• When mode is vega, the data is put in an array of length 1. When it's vega-lite it stays as an object.

Hopefully this makes it less brittle, but I'm happy to change the way it sends the message to the editor as you mentioned - I'm just not clear exactly what I need to change there yet.

[domoritz]

This isn't an easy issue so I don't want you to get too hung up when working on it and I will help where I can.

When I say send the state, I mean use https://vega.github.io/vega/docs/api/view/#view_getState in embed and https://vega.github.io/vega/docs/api/view/#view_setState in the editor. You will need to send a pull request to the editor as well.

I had issues with serializing state before so maybe we also need to change Vega to make this approach work.

[domoritz]

Data can be nested in a spec so this code won't work in general.

[domoritz]

Please send a new pull request.