transpose(object)? about d3-array

[Fil]

I think it would be useful under the same name transpose, but with that name it absolutely must be involutive, ie transpose back [ {year: 2001, value: 1}, {year: 2002, value: 2}] to {year: [2001, 2002], value: [1, 2]}. Which makes auto-detection a bit harder (array of array, array of objects, object of arrays).
I've made a few tests here https://observablehq.com/d/e546523c2f1fbe2f

[mbostock]

Perhaps it’s worth introducing two new methods: one for converting an array of objects to an object of arrays, and another for converting an object of arrays to an array of objects. Somewhat related, there’s also been a discussion on a pivot operation #142.

[Fil]

Since there does not seem to be a conflict of definitions, I prefer to use transpose for the four cases: arrays of arrays [[]], arrays of objects [{}], objects of arrays {[]} and objects of objects {{}}.
#158