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Add support for custom histogram min/max limits #15

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4 changes: 2 additions & 2 deletions README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -120,10 +120,10 @@ Calculate the [standard deviation](http://en.wikipedia.org/wiki/Standard_deviati

Calculate the value representing the desired [percentile](http://en.wikipedia.org/wiki/Percentile) `(0 < ptile <= 1)`. Uses the Estimation method to interpolate non-member percentiles.

`histogram(vals[, bins])`
`histogram(vals[, bins[, binLimits]])`
---

Build a histogram representing the distribution of the data in the provided number of `bins`. If `bins` is not set, it will choose one based on `Math.sqrt(vals.length)`. Data will look like:
Build a histogram representing the distribution of the data in the provided number of `bins`. If `bins` is not set, it will choose one based on `Math.sqrt(vals.length)`. `binLimits` can be used to define custom min/max edges for the bins (as an array with two numeric values). Data will look like:
```
histogram {
values: [ 86, 159, 253, 335, 907, 405, 339, 270, 146, 100 ],
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8 changes: 4 additions & 4 deletions stats.js
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Expand Up @@ -154,7 +154,7 @@ function percentile(vals, ptile) {
return (1 - fract) * vals[int_part] + fract * vals[Math.min(int_part + 1, vals.length - 1)]
}

function histogram (vals, bins) {
function histogram(vals, bins, binLimits) {
if (vals == null) {
return null
}
Expand All @@ -171,8 +171,8 @@ function histogram (vals, bins) {
bins = 1
}

var min = vals[0]
var max = vals[vals.length - 1]
var min = binLimits ? binLimits[0] : vals[0]
var max = binLimits ? binLimits[1] : vals[vals.length - 1]
if (min === max) {
// fudge for non-variant data
min = min - 0.5
Expand All @@ -182,7 +182,7 @@ function histogram (vals, bins) {
var range = (max - min)
// make the bins slightly larger by expanding the range about 10%
// this helps with dumb floating point stuff
var binWidth = (range + (range * 0.05)) / bins
var binWidth = (range + (range * (binLimits ? 0 : 0.05))) / bins
var midpoint = (min + max) / 2
// even bin count, midpoint makes an edge
var leftEdge = midpoint - (binWidth * Math.floor(bins / 2))
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8 changes: 8 additions & 0 deletions test/index.js
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Expand Up @@ -234,6 +234,14 @@ test('histogram', (t) => {
}
t.deepEquals(histogram([-100, -53, 10, 100, -22, 0, 0, 1, 3, 44], 20), expect, 'range goes from negative to positive')

expect = {
binLimits: [0, 9],
binWidth: 1.5,
bins: 6,
values: [1, 2, 1, 2, 0, 0],
}
t.deepEquals(histogram([1, 2, 3, 4, 5, 6], 6, [0, 9]), expect, 'custom bin limits')

function diceTest (n, dieString) {
var rolls = []
for (var i = 0; i < n; i++) {
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