enh: Support selector and ds.summary for geom_aggregator

[hoxbro]

Resolves #6736
Resolves #6739

Mostly factoring out logic in aggregate to also use for geom_aggregate. Not sure if I like the new method name, but just wanted to push this before it was lost in a stash. Know at least one test is failing because of change of NdOverlay to ImageStack.

Summary

import datashader as ds

import holoviews as hv
from holoviews.operation.datashader import rasterize

hv.extension("bokeh")

rects = hv.Rectangles(
    [
        (0, 0, 1, 1, 128, 100, 200),
        (2, 3, 4, 6, 100, 50, 80),
        (0.5, 2, 1.5, 4, 20, 200, 120),
        (2, 1, 3.5, 2.5, 110, 40, 240),
    ],
    kdims=[
        hv.Dimension("x0"),
        hv.Dimension("y0"),
        hv.Dimension("x1"),
        hv.Dimension("y1"),
    ],
    vdims=[
        hv.Dimension("r"),
        hv.Dimension("g"),
        hv.Dimension("b"),
    ],
)
rasterize(
    rects,
    aggregator=ds.summary(
        r=ds.where(ds.max("x0"), "r"),
        g=ds.where(ds.max("x0"), "g"),
        b=ds.where(ds.max("x0"), "b"),
    ),
).opts(tools=["hover"])

Screencast.From.2025-11-24.19-06-59.mp4

Selector

import datashader as ds
import numpy as np
import pandas as pd

import holoviews as hv
from holoviews.operation.datashader import datashade, dynspread, rasterize

hv.extension("bokeh")

# Set default hover tools on various plot types
hv.opts.defaults(tools=["hover"])

rects = hv.Rectangles(
    [(0, 0, 1, 1), (2, 3, 4, 6), (0.5, 2, 1.5, 4), (2, 1, 3.5, 2.5)],
    kdims=[
        hv.Dimension("Time"),
        hv.Dimension("y0"),
        hv.Dimension("x1"),
        hv.Dimension("y1"),
    ],
)

rects = datashade(rects, aggregator=ds.count(), selector=ds.min("Time"))
rects.opts(hover_tooltips=["Time"])
rects

Screencast.From.2025-11-24.19-07-53.mp4

Simple

import datashader as ds

import holoviews as hv
from holoviews.operation.datashader import rasterize

hv.extension("bokeh")

rects = hv.Rectangles(
    [
        (0, 0, 1, 1, 128, 100, 200),
        (2, 3, 4, 6, 100, 50, 80),
        (0.5, 2, 1.5, 4, 20, 200, 120),
        (2, 1, 3.5, 2.5, 110, 40, 240),
    ],
    kdims=[
        hv.Dimension("x0"),
        hv.Dimension("y0"),
        hv.Dimension("x1"),
        hv.Dimension("y1"),
    ],
    vdims=[
        hv.Dimension("r"),
        hv.Dimension("g"),
        hv.Dimension("b"),
    ],
)
rasterize(rects, aggregator=ds.max("x0")).opts(tools=["hover"])

Screencast.From.2025-11-24.19-08-25.mp4

[codecov]

Codecov Report

❌ Patch coverage is 97.88732% with 3 lines in your changes missing coverage. Please review.
✅ Project coverage is 89.21%. Comparing base (ec851b7) to head (8758382).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
holoviews/operation/datashader.py	97.08%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6743      +/-   ##
==========================================
+ Coverage   87.83%   89.21%   +1.37%     
==========================================
  Files         332      332              
  Lines       72010    72063      +53     
==========================================
+ Hits        63250    64291    +1041     
+ Misses       8760     7772     -988     

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[hoxbro]

This is duplicated, but I think it is OK.