This is an amazing addition. Thanks @yohai

thanks @yohai!

It looks like the merge went OK, but you have a couple of tests that are failing. Click on the "Travis-CI" link above next to the red "X" to see details: https://travis-ci.org/pydata/xarray/jobs/386973465

OK, somehow the rebasing thing broke everything and I am at a loss. @shoyer, @dcherian please guide me on how to proceed. Sorry.

Thanks @shoyer. I fixed everything except for the coverall part, which is weird. The lines it marks as untested are the function _line_facetgrid, which the main function that performs all of the testing. I suspect that it simply doesn't run my new tests for some reason. When I run pytest locally these lines do get tested (I verified by adding print commands there). Should I add decorators like pytest.mark.somethingfor coverall to notice these tests?

The specific problematic lines are those marked red in coveralls, e.g., https://coveralls.io/builds/17253745/source?filename=xarray%2Fplot%2Fplot.py#L101 https://coveralls.io/builds/17253745/source?filename=xarray%2Fplot%2Fplot.py#L176 https://coveralls.io/builds/17253745/source?filename=xarray%2Fplot%2Fplot.py#L291

These are all cases where an error is raised.

Thanks @shoyer. I fixed everything except for the coverall part, which is weird. The lines it marks as untested are the function _line_facetgrid, which the main function that performs all of the testing. I suspect that it simply doesn't run my new tests for some reason. When I run pytest locally these lines do get tested (I verified by adding print commands there). Should I add decorators like pytest.mark.somethingfor coverall to notice these tests?

I wrote some tests and also followed @shoyer's suggestion to make the plots look more like seaborn. Here's what it looks like now:

I also had to refactor the code adding legend to a line plot to avoid duplicities.

writing new functions that will verify that stuff works as it should

Yes. See here for example tests for FacetGrid. Testing plotting functions is not trivial but we usually test only very basic functionality. You might find some examples in here.

or that the new addition does not mess up previous plotting behavior?

This is usually covered by continuous integration, which already ran the tests on your current PR (the "all checks have passed" green button above). So on this side you are safe for now, unless our previous tests weren't efficient enough ;-)

@jhamman @shoyer Sorry for being a noob, but what exactly do you mean by "add some basic unit tests"? you mean writing new functions that will verify that stuff works as it should, or that the new addition does not mess up previous plotting behavior?

@yohai - this looks great. Can we add some basic unit tests covering this functionality?

was simpler than I thought. @shoyer I added the plots.

Example code to demonstrate functionality:

```python import xarray as xr import numpy as np import pandas as pd

np.random.seed(0) tm = pd.date_range('2000-01-01', end='2000-01-02', freq='H') d4 = xr.DataArray(np.random.randn(len(tm), 6, 3, 3), dims=['time', 'x', 'text_dim', 'z'], coords=[tm, range(6), ['foo', 'bar', 'foobar'], [3.5, 4.9, 6.7]], name='arr_name') d3 = d4[..., 0].drop('z') d2 = d3[..., 0].drop('text_dim')

generate a faceted 4-dimensional plot:

d4.plot(hue='text_dim', col='x', row='z')

or equivalently:

d4.plot.line(x='time', col='x', row='z')

````

python d3.plot(col='x', row='text_dim')

python d2.plot(hue='x')

python d3.plot.line(col='x', col_wrap=3, hue='text_dim')

I found some bugs. I'll reopen when I fix them.

I'm really excited about this!

Could you kindly paste in examples of what the generated plots look like in your comment? (GitHub will upload an image when you paste it in.)