altairflow.py

import math, random, os
from metaflow import step, FlowSpec, card

class AltairFlow(FlowSpec):

    @card(type='html')
    @step
    def start(self):
        import altair as alt
        from vega_datasets import data
        
        source = data.seattle_weather()

        scale = alt.Scale(domain=['sun', 'fog', 'drizzle', 'rain', 'snow'],
                        range=['#e7ba52', '#a7a7a7', '#aec7e8', '#1f77b4', '#9467bd'])
        color = alt.Color('weather:N', scale=scale)

        # We create two selections:
        # - a brush that is active on the top panel
        # - a multi-click that is active on the bottom panel
        brush = alt.selection_interval(encodings=['x'])
        click = alt.selection_multi(encodings=['color'])

        # Top panel is scatter plot of temperature vs time
        points = alt.Chart().mark_point().encode(
            alt.X('monthdate(date):T', title='Date'),
            alt.Y('temp_max:Q',
                title='Maximum Daily Temperature (C)',
                scale=alt.Scale(domain=[-5, 40])
            ),
            color=alt.condition(brush, color, alt.value('lightgray')),
            size=alt.Size('precipitation:Q', scale=alt.Scale(range=[5, 200]))
        ).properties(
            width=550,
            height=300
        ).add_selection(
            brush
        ).transform_filter(
            click
        )

        # Bottom panel is a bar chart of weather type
        bars = alt.Chart().mark_bar().encode(
            x='count()',
            y='weather:N',
            color=alt.condition(click, color, alt.value('lightgray')),
        ).transform_filter(
            brush
        ).properties(
            width=550,
        ).add_selection(
            click
        )

        chart = alt.vconcat(
            points,
            bars,
            data=source,
            title="Seattle Weather: 2012-2015"
        )

        self.html = chart.to_html()
        self.next(self.end)


    @step
    def end(self):
        pass

if __name__ == '__main__':
    AltairFlow()