Adding a bin shorthand

Would it be possible to add a shorthand syntax for binning? The exact proposal would be to to allow to replace

alt.Chart(cars).mark_bar().encode(
    x=alt.X("Horsepower", bin=True), 
    y="count()"
)

by

alt.Chart(cars).mark_bar().encode(
    x="bin(Horsepower)", 
    y="count()"
)

After reading through #763 I understand that changes in this direction are not trivial, but I would suppose that just allowing this simple substitution would not break the conceptual model, as one would still have to use alt.X to customize the binning. However, for the default case this substitution should correspond to what is already being done for aggregations.

[jakevdp]

How often do people use this?

Not much, if at all. We don’t do any direct property access in Altair’s docs or examples, so I think it’s a pretty minor incompatibility all told. And my take is it’s well worth the benefit of being able to do this:

chart.encode(
  x = alt.X('name:Q').bin(maxbins=100).axis(title=None).scale(None)
)

instead of this:

chart.encode(
  x = alt.X('name:Q',
    bin=alt.Bin(maxbins=100),
    axis=alt.Axis(title=None),
    scale=None
  )
)

[jakevdp]

Prototype & more discussion in #1629