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