Constraints that specify single values

Say we want to select all passes. We can do it like this:

import numpy as np
import pandas as pd
import xarray as xr
import xarray_events

ds = xr.Dataset(
    data_vars={
        'ball_trajectory': (
            ['frame', 'cartesian_coords'],
            np.exp(np.linspace((-6, -8), (3, 2), 2450))
        )
    },
    coords={
        'frame': np.arange(1, 2451),
        'cartesian_coords': ['x', 'y'],
        'player_id': [2, 3, 7, 19, 20, 21, 22, 28, 34, 79]
    },
    attrs={'match_id': 12, 'resolution_fps': 25}
)

events = pd.DataFrame(
    {
        'event_type':
            ['pass', 'goal', 'pass', 'pass', 'pass',
             'penalty', 'goal', 'pass', 'pass', 'penalty'],
        'start_frame': [1, 425, 600, 945, 1100, 1280, 1890, 2020, 2300, 2390],
        'end_frame': [424, 599, 944, 1099, 1279, 1889, 2019, 2299, 2389, 2450],
        'player_id': [79, 79, 19, 2, 3, 2, 3, 79, 2, 79]
    }
)

(
    ds
    .events.load(events, {'frame': ('start_frame', 'end_frame')})
    .events.sel({'event_type': 'pass'})
    .events.df
)

	event_type	start_frame	end_frame	player_id
0	pass	1	424	79
2	pass	600	944	19
3	pass	945	1099	2
4	pass	1100	1279	3
7	pass	2020	2299	79
8	pass	2300	2389	2

See? We are now using the accessor twice, once every time we need to access any of its methods. First we access the method sel() and then the property df(). This is because the result of sel() is actually a (stateful) Dataset, as mentioned before, so we use the accessor again on it in a chain-like fashion. Very convenient!

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