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Indexing

Indexing#

Boost-histogram implements the UHI indexing protocol. You can read more about it on the UHI Indexing page.

Boost-histogram specific details#

Boost-histogram implements bh.loc, builtins.sum, bh.rebin, bh.underflow, and bh.overflow from the UHI spec. A bh.tag.at locator is provided as well, which simulates the Boost.Histogram C++ .at() indexing using the UHI locator protocol.

Boost-histogram allows “picking” using lists, similar to NumPy. If you select with multiple lists, boost-histogram instead selects per-axis, rather than group-selecting and reducing to a single axis, like NumPy does. You can use bh.loc(...) inside these lists.

Example:

h = bh.histogram(
    bh.axis.Regular(10, 0, 1),
    bh.axis.StrCategory(["a", "b", "c"]),
    bh.axis.IntCategory([5, 6, 7]),
)

minihist = h[:, [bh.loc("a"), bh.loc("c")], [0, 2]]

# Produces a 3D histgoram with Regular(10, 0, 1) x StrCategory(["a", "c"]) x IntCategory([5, 7])

This feature is considered experimental in boost-histogram 1.1.0. Removed bins are not added to the overflow bin currently.

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