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""" |
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Atmospheric CO2 Concentration |
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----------------------------- |
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This example is a fully developed line chart that uses a window transformation. |
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It was inspired by `Gregor Aisch's work at datawrapper |
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<https://www.datawrapper.de/_/OHgEm/>`_. |
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""" |
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import altair as alt |
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from vega_datasets import data |
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source = data.co2_concentration.url |
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base = alt.Chart( |
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source, |
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title="Carbon Dioxide in the Atmosphere" |
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).transform_calculate( |
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year="year(datum.Date)" |
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).transform_calculate( |
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decade="floor(datum.year / 10)" |
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).transform_calculate( |
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scaled_date="(datum.year % 10) + (month(datum.Date)/12)" |
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).transform_window( |
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first_date='first_value(scaled_date)', |
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last_date='last_value(scaled_date)', |
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sort=[{"field": "scaled_date", "order": "ascending"}], |
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groupby=['decade'], |
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frame=[None, None] |
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).transform_calculate( |
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end="datum.first_date === datum.scaled_date ? 'first' : datum.last_date === datum.scaled_date ? 'last' : null" |
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).encode( |
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x=alt.X( |
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"scaled_date:Q", |
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axis=alt.Axis(title="Year into Decade", tickCount=11) |
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), |
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y=alt.Y( |
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"CO2:Q", |
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title="CO2 concentration in ppm", |
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scale=alt.Scale(zero=False) |
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) |
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) |
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line = base.mark_line().encode( |
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color=alt.Color( |
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"decade:O", |
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scale=alt.Scale(scheme="magma"), |
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legend=None |
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) |
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) |
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text = base.encode(text="year:N") |
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start_year = text.transform_filter( |
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alt.datum.end == 'first' |
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).mark_text(baseline="top") |
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end_year = text.transform_filter( |
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alt.datum.end == 'last' |
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).mark_text(baseline="bottom") |
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(line + start_year + end_year).configure_text( |
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align="left", |
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dx=1, |
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dy=3 |
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).properties(width=600, height=375) |
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