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Fix histogram bin redistribution dropping counts at the range boundary #7139

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Fix histogram bin redistribution dropping counts at the range boundary #7139

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8 changes: 7 additions & 1 deletion tensorboard/webapp/widgets/histogram/histogram_util.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -119,8 +119,14 @@ function rebuildBins(bins: Bin[], range: Range, binCount: number): Bin[] {
let nextBinContribution = 0;
for (let i = 0; i < binCount; i++) {
const resultLeft = left + i * dx;
const resultRight = resultLeft + dx;
const isLastResultBin = i === binCount - 1;
// The last result bin must extend exactly to `range.right`. Computing it as
// `resultLeft + dx` accumulates floating-point error in the repeated `i * dx`
// sum and can land just below `range.right`; an input bin whose right edge
// sits exactly on `range.right` then satisfies `bin.x + bin.dx > resultRight`
// and is skipped without being consumed, dropping its counts. Clamp the last
// result bin's right edge to `range.right` so those counts are preserved.
const resultRight = isLastResultBin ? right : resultLeft + dx;

let resultY = nextBinContribution;
nextBinContribution = 0;
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32 changes: 32 additions & 0 deletions tensorboard/webapp/widgets/histogram/histogram_util_test.ts
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Expand Up @@ -54,6 +54,38 @@ describe('histogram util', () => {
});
});

describe('count conservation at the range boundary', () => {
function totalCount(bins: Bin[]): number {
return bins.reduce((sum, bin) => sum + bin.y, 0);
}

it('preserves a bin whose right edge sits on range.right', () => {
// A zero-width bin at x=1 sits exactly on the range's right edge (the
// widest histogram spans [0, 1]). It must not be dropped when the bins
// are redistributed into `binCount` result bins.
const input: Bin[] = [
{x: 0, dx: 1, y: 1},
{x: 1, dx: 0, y: 5},
];
const [result] = histogramsToBins(
buildNormalizedHistograms([binsToHistogram(input)], 6)
);
expect(totalCount(result)).toBeCloseTo(totalCount(input), 6);
});

it('preserves counts when the final normal bin ends on range.right', () => {
const input: Bin[] = [
{x: 0, dx: 1, y: 2},
{x: 1, dx: 1, y: 3},
{x: 2, dx: 1, y: 4},
];
const [result] = histogramsToBins(
buildNormalizedHistograms([binsToHistogram(input)], 7)
);
expect(totalCount(result)).toBeCloseTo(totalCount(input), 6);
});
});

describe('single histogram', () => {
it('converts a 0 width bin into a default bin', () => {
expect(
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