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"""
The U.S. Employment Crash During the Great Recession
----------------------------------------------------
This example is a fully developed bar chart with negative values using the sample dataset of U.S. employment changes during the Great Recession.
"""
# category: case studies
import altair as alt
import pandas as pd
from vega_datasets import data
source = data.us_employment()
presidents = pd.DataFrame([
{
"start": "2006-01-01",
"end": "2009-01-19",
"president": "Bush"
},
{
"start": "2009-01-20",
"end": "2015-12-31",
"president": "Obama"
}
])
bars = alt.Chart(
source,
title="The U.S. employment crash during the Great Recession"
).mark_bar().encode(
x=alt.X("month:T", title=""),
y=alt.Y("nonfarm_change:Q", title="Change in non-farm employment (in thousands)"),
color=alt.condition(
alt.datum.nonfarm_change > 0,
alt.value("steelblue"),
alt.value("orange")
)
)
rule = alt.Chart(presidents).mark_rule(
color="black",
strokeWidth=2
).encode(
x='end:T'
).transform_filter(alt.datum.president == "Bush")
text = alt.Chart(presidents).mark_text(
align='left',
baseline='middle',
dx=7,
dy=-135,
size=11
).encode(
x='start:T',
text='president',
color=alt.value('#000000')
)
(bars + rule + text).properties(width=600)
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