Hist

Overview

Use this skill to build and manipulate hist.Hist objects, choose axis/storage types, fill with data and weights, and produce publication-style plots with mplhep styles, all based on matplotlib.

Quick start

• Create histograms with

  Hist.new

  plus axis builders (

  Reg

  ,

  Var

  ,

  StrCat

  ) and finish with exactly one storage (

  Int64

  or

  Weight

  ).
• Make sure axis labels contain a short variable name and units. Histogram titles should contains a slightly longer concise description of what data went into the plot.
• Fill with

  .fill(...)

  using axis names; note that

  .fill

  returns

  None

  .
• Slice or project with UHI indexing (e.g.,

  h.project("x")

  or

  h[{"x": 5j}]

  ).
• Plot with

  hist.plot(...)

  or

  mplhep.hist2dplot(...)

  ; use

  plt.style.use(hep.style.ATLAS)

  for HEP-style plots.

Core tasks

Create axes and storage

• Use

  Reg

  for uniform bins and

  Var

  for variable-width bins.
• Use

  StrCat

  for categorical axes; set

  growth=True

  for auto-added categories.
• Choose storage:

  Int64

  for unweighted counts,

  Weight

  for weighted fills.

Fill and access contents

• Fill with named axes (e.g.,

  h.fill(x=..., y=..., weight=...)

  ).
• Read counts with

  h.view()

  and errors from

  np.sqrt(h.variances())

  .

Slice, rebin, and project

• Use UHI slicing (complex numbers for bin selection,

  ::2j

  for rebinning).
• Project with

  h.project("axis_name")

  for 1D plots.

Plot and save

• Use

  hist.plot(histtype="fill")

  for 1D; use

  mplhep.hist2dplot

  for 2D.
• Use

  plt.subplots()

  without custom

  figsize

  unless explicitly requested.
• Save with

  fig.savefig("name.png")

  and close with

  plt.close(fig)

  .

References

• Use

  references/hist-hints.md

  for concrete code snippets and common patterns.
• Use

  references/hist-advanced.md

  for UHI indexing, plotting gotchas, and label/LaTeX guidance.
• Use

  references/lhc-hist-ranges.md

  for starting suggestions on histogram axis ranges and binning.