marker() should place marker at bin center

[lukasheinrich]

I'm trying to generate a standard HEP plot: stacks of simulated estimates overlaid with data points.

import histbook

array = numpy.random.normal(0, 1, 100)
histogram1 = Hist(bin("data", 10, -5, 5))
histogram1.fill(data=array)

array = numpy.random.normal(1, 1, 100)
histogram2 = Hist(bin("data", 10, -5, 5))
histogram2.fill(data=array)

array = numpy.random.normal(0, 1, 100)
data_hist = Hist(bin("data", 10, -5, 5))
data_hist.fill(data=array)

group = Hist.group(by='sample', h1 = histogram1, h2 = histogram2)
group.stack("sample").area("data").to(canvas)
overlay(group.stack("sample").area("data"), data_hist.marker()).to(canvas)

the results I get, looks like it's doing the right thing, but the markers for the data histogram are on the bin edge. I think it would be more intuitive if they were in the bin center (also if there were some more styling option, I'd plot is as black filled circular markers)

[jpivarski]

Something's broken because there's explicit code to make the points go in the center, not the edges. I'll take a look.

For the plot style, I'm letting Vega-Lite choose things, rather than try to strong-arm it. The marker method has a markerstyle option that passes directly into the Vega-Lite JSON. I haven't played with it to find out if it gives the user enough freedom or if another handle will be necessary.

[jpivarski]

As it turns out, I didn't really have code to handle that case. I was handling a similar case and misremembered. It's fixed now.