Interpolate typed arrays?

[Mike Bostock]

It’d be nice if there were an interpolator for typed arrays, like Float32Array. The existing d3.interpolateArray is almost what we want—the only change you’d need to make is to say c = new b.constructor(nb) rather than c = new Array(nb).

However, there are two considerations with this approach:

• Should d3.interpolate delegate to d3.interpolateArray if b is a typed array? If so, we will need to use a different test than Array.isArray that also returns true for typed arrays.

• How should d3.interpolateArray behave if b is not an array and not a typed array? The current implementation is guaranteed to return an Array even if b is not an array (but may be an array-like). If c is constructed using b.constructor, the change to d3.interpolateArray might be considered backwards-incompatible.

It might make more sense to introduce a new d3.interpolateTypedArray, and keep the current behavior of d3.interpolateArray. And we could optionally extend d3.interpolate to delegate to d3.interpolateTypedArray for typed array input. Seems like the following test would work:

function isTypedArray(x) {
  return ArrayBuffer.isView(x) && !(x instanceof DataView);
}

[Chad Brockman]

Hey @mbostock -- any thoughts on typed array support? We have a lot of "bulk" data we'd like to be about to pass directly to D3...

[Philippe Rivière]

interpolateArray would not handle typed arrays with 10 or 100 millions of rows. Indeed above 1e6 values it starts to crumble.

An implementation with typed arrays:
https://observablehq.com/d/4a42579f12a84f89

[Philippe Rivière]

@chadbr please see the pull-request #65 and test at https://observablehq.com/d/d966cf85471db4f7

[Chad Brockman]

@Fil awesome :)

[Mike Bostock]

Added interpolateNumberArray and typed array detection in #77.