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.. currentmodule:: altair
.. _user-guide-pivot-transform:
Pivot
~~~~~
The pivot transform is, in short, a way to convert long-form data to wide-form
data directly without any preprocessing (see :ref:`data-long-vs-wide` for more
information). Pivot transforms are useful for creating matrix or cross-tabulation
data, acting as an inverse to the :ref:`user-guide-fold-transform`.
Here is an example, using Olympic medals data:
.. altair-plot::
import altair as alt
import pandas as pd
df = pd.DataFrame.from_records([
{"country": "Norway", "type": "gold", "count": 14},
{"country": "Norway", "type": "silver", "count": 14},
{"country": "Norway", "type": "bronze", "count": 11},
{"country": "Germany", "type": "gold", "count": 14},
{"country": "Germany", "type": "silver", "count": 10},
{"country": "Germany", "type": "bronze", "count": 7},
{"country": "Canada", "type": "gold", "count": 11},
{"country": "Canada", "type": "silver", "count": 8},
{"country": "Canada", "type": "bronze", "count": 10}
])
alt.Chart(df).transform_pivot(
'type',
groupby=['country'],
value='count'
).mark_bar().encode(
x='gold:Q',
y='country:N',
)
The pivot transform, when combined with other elements of the Altair grammar, enables some
very interesting chart types. For example, here we use pivot to create a single tooltip for
values on multiple lines:
.. altair-plot::
import altair as alt
from vega_datasets import data
source = data.stocks()
base = alt.Chart(source).encode(x='date:T')
columns = sorted(source.symbol.unique())
selection = alt.selection_point(
fields=['date'], nearest=True, on='mouseover', empty=False, clear='mouseout'
)
lines = base.mark_line().encode(y='price:Q', color='symbol:N')
points = lines.mark_point().transform_filter(selection)
rule = base.transform_pivot(
'symbol', value='price', groupby=['date']
).mark_rule().encode(
opacity=alt.condition(selection, alt.value(0.3), alt.value(0)),
tooltip=[alt.Tooltip(c, type='quantitative') for c in columns]
).add_params(selection)
lines + points + rule
Transform Options
^^^^^^^^^^^^^^^^^
The :meth:`~Chart.transform_pivot` method is built on the :class:`~PivotTransform`
class, which has the following options:
.. altair-object-table:: altair.PivotTransform
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