expose ordering predicate

[gordonwoodhull]

Now that we are using built-in Array.sort, we could expose an ordering predicate instead of only .ordering().

.ordering() makes it difficult to sort descending, for example.

This replaces #1161, which I overexplained and made too complicated.

[gordonwoodhull]

If the predicate is specified, it would have precedence over the ordering accessor.

Currently we have

https://github.com/dc-js/dc.js/blob/92c897a47acc333c2c11fd1f2ca7ca69c0886429/src/base/base-mixin.js#L363-L366

This could be

 _computeOrderedGroups (data) { 
     // clone the array before sorting, otherwise Array.sort sorts in-place
     const defaultPredicate = (a, b) => this._ordering(a) - this._ordering(b); 
     return Array.from(data).sort(_orderPredicate || defaultPredicate); 
 } 

and then add a getter/setter orderPredicate.

[cwolcott]

How you thought anymore about implementing something like this. I have a mixed case of keys and would like to sort by case insensitive order.

An example of my keys are: all, Anyone, lightning, Thunder

The order in the html-legend is: Anyone, Thunder, all, lightning

[gordonwoodhull]

It should be easy - want to give it a shot?

Case insensitivity would be an excellent test case.

Just don’t read #1161 - that made it sound much too complicated. It should just be the one line change above.