docs: MVP plotly-express docs

[alexpeters1208]

Minimum required docs for the plotly-express plugin. Here are the outstanding items:

1. Fill out "other".
2. Document ecdf once it is implemented.

Directions for testing:

As of 7/17, everything needed for testing is baked into a release. Here's a simple testing environment using pip-installed DH.

# make new dir for testing
mkdir test-dx && cd test-dx

# create env for installs
python -m venv test-dx-venv
source test-dx-venv/bin/activate

# install some necessary things for the build
pip install --upgrade pip setuptools

# install the server, need 35.1 or 34.3
pip install deephaven-server==0.35.1

# install the plugin
pip install deephaven-plugin-plotly-express

# I need to do this to get `which deephaven` to give the correct venv version, you may not
deactivate
source test-dx-venv/bin/activate

# start the server
deephaven server

[dsmmcken]

nothing huge jumps out on first read. I haven't tried running every block of code. @jnumainville should look through with sharper eyes on the code blocks.

[chipkent]

This example is identical to the prior example and is not doing what it says it does.

[alexpeters1208]

I didn't notice this initially. Getting the example "right" gives some pretty bad results. Putting the code in but leaving this comment open.

[alexpeters1208]

#665

[dsmmcken]

Sorry - I hadn't mentioned this previously but one of the reasons I pushed for all our example data sets to be deterministic was for testing. This one example is not.

[chipkent]

This needs a ticket to assess the library. It is not a problem with your example.

[chipkent]

Take this example:

import deephaven.plot.express as dx
gapminder = dx.data.gapminder() # import a ticking version of the Gapminder dataset

# get a specific country
brazil = gapminder.where("country == `Brazil`")

# specify multiple y-axis columns and order axes left to right with yaxis_sequence
line_plot_multi = dx.line(brazil, x="year", y=["pop", "gdpPercap"], yaxis_sequence=[1, 2])
line_plot_multi_2 = dx.line(brazil, x="year", y=["pop", "gdpPercap"])

Passing multiple value to y is NOT how the multiple axes are created. That creates two lines. To create separate axes for the lines, you need to specify yaxis_sequence. This interaction is not clear in the prose or example. The example would be better with two plots like I have. Show that providing y=[a,b] gives two lines, and then adding yaxis_sequence puts them on different axes. As it is, the prose is incorrect and doesn't show them how to do these two common cases.

[jnumainville]

it should be clarified that by is not simply an alias for color
it can be tweaked by using by_vars and passing in these other columns such as symbol and size
it also behaves slightly differently though, take this example

import deephaven.plot.express as dx
tips = dx.data.tips() # import the example iris data set

by_list = dx.scatter(tips, x="TotalBill", y="Tip", by=["Time", "Smoker"], by_vars=["color", "symbol"])
by_prod = dx.scatter(tips, x="TotalBill", y="Tip", by="Time", symbol="Smoker")

by_list just loops through color/symbol combos (jointly)
whereas by_prod assigns colors to specific column values, so, of the four joint values, Lunch and Dinner have the same color and Yes and No have the same symbol.

The first method is more useful to emphasize differences, whereas the second is more useful to emphasize similarities.

[alexpeters1208]

I removed the "for which by" is an alias" part - hopefully that cleans up the confusion. As far as using by_vars, that seems like something that should belong in the expanded version of this doc once the full thing is written, and not necessarily in the introduction. What do you think?

[jnumainville]

Yeah, shouldn't be in the intro, that's fine

[chipkent]

Ultimately, partition_by should be linked, but I don't know that @dsmmcken is far enough down the new impl to worry about this yet.