Rather than specifying an orientation, compute the layout in normalized space. In a future change,
I'd also like to clean up the temporary state that is stored on tree nodes, and record dx and dy
attributes per node that could be used to compute a space-filling layout.
The treemap layout can now be set to "sticky" mode, which preserves the row
arrangements from an earlier layout. This is particularly handy for animating
treemaps, as it avoids the temporary occlusion as nodes swap positions. Thanks
to @philogb and the New York Times for the inspiration!
This fixes a bug in the pie layout sorting where we want the sort order to
affect the layout, but not the order in which arcs are rendered—and furthermore
we want the order of arcs to always match the order of data. (If you want to
sort the data, do that before it is passed to the layout.)
This adds d3.layout.pie, which can be used to compute the start and end angles
for arcs given an arbitrary array of data. In addition, d3.svg.arc now has a
`centroid` method that computes the center of the arc, useful for labeling.
Together these changes greatly simplify the donut & pie examples.
This commit also includes a `map` method for selections, which is similar to the
`filter` method. This allows you to map the data bound to the current selection.
I'm not currently using it, but it seems like a useful feature for those cases
where you want to rebind the current selection to different (but related) data.
The renaming of attributes is totally not worth the hassle of maintaining an
externs file (or using the awkward `foo["bar"]` syntax). The file size
reduction from the advanced optimizations was negligible, besides!
Mike Bostock
Jason Davies