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histogram: numeric bars are a percentage of the bucketed values, the NA bar a percentage of all rows

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Assessment

Difficulty
2/5
Estimated time
1-3 hours
Newbie friendliness
75/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Active
Tech stack
pandas, python
Domain
data-visualization

Research direction

Start with numeric_histogram in histogram.py at the referenced line, and compare its population calculation with categorical_histogram; the issue notes that Polars shares this implementation. Check how the bucketed values and null count are calculated, then verify that bucket and NA bars use the same percentage base, including the example with 90% nulls; tail handling is also relevant to #1078.

Written by the indexing model from the issue text.

Description

Histograms

Problem

numeric_histogram (histogram.py:148) draws each bucket as its share of the bucketed values (normalized_populations sums to 1 over the middle of the column) and the NA bar as nan_per * 100 (line 132), a share of all rows. The bars share one y axis, so a column that's 90% null shows ten buckets of about 10 beside an NA bar of 90, where each bucket holds about 1% of the rows. categorical_histogram divides both by length, so a categorical column with the same null share has its bars on one base.

import pandas as pd
from buckaroo.customizations.pd_stats_v2 import PD_ANALYSIS_V2
from buckaroo.pluggable_analysis_framework.stat_pipeline import StatPipeline

def histo(values):
    sd, _ = StatPipeline(PD_ANALYSIS_V2, unit_test=False).process_df(pd.DataFrame({"a": values}))
    return sd["a"]["histogram"]

h = histo([None] * 900 + [float(i) for i in range(100)])
print(sum(b.get("population", 0) for b in h), [b for b in h if "NA" in b])
# 98.0 [{'name': 'NA', 'NA': 90.0}]
print(histo([None] * 900 + ["x", "y"] * 50))
# [{'name': 'x', 'cat_pop': 5.0}, {'name': 'y', 'cat_pop': 5.0}, {'name': 'NA', 'NA': 90.0}]

Polars shares numeric_histogram and does the same.

Suggested fix

Scale the bucket populations by the share of rows that were bucketed, so every bar is a percentage of the column. The tails would need the same base (see #1078).

Context

Found while probing histogram edge cases after #1069. Reproduces on main at e88ace91.

Dominant language
Python
Stars
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Forks
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Avg merge
21h 26m
Merged PRs (30d)
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