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/**
* Inverse operation of linear interpolation. Given a range and a
* value, returns the interpolation amount to get that value.
*
* @param min Lowest value in the range
* @param max Highest value in the range
* @param value Value in the range
* @returns Interpolation amount from 0.0 to 1.0 (or beyond if `x` is outside the range [min, max])
*/
export function inverseLinearInterpolation(min: number, max: number, value: number): number {
if (min === max) {
return 0;
}
return (value - min) / (max - min);
}
/**
* Create a function that calculates a GitHub heat index based on a list of numbers.
* The list is used to find the min and max of the range. The function can then
* calculate a heat index for a given value based on that range.
*
* GitHub has 10 heat values, and uses a lower heat index for a higher value. So the
* highest heat index that will be returned is 1, and the lowest is 10.
*
* @param numbers values to use to calculate the min and max of the heat range
* @returns function to calculate heat index of a given number
*/
export function createHeatIndexFunction(numbers: number[]): (value: number) => number {
const steps = 10; // GH has 10 heat colors
const min = Math.min(...numbers);
const max = Math.max(...numbers);
return (value: number) => {
// Inverse linear interpolation figures out how far the value is between min & max
const interp = Math.max(0, Math.min(1, inverseLinearInterpolation(min, max, value)));
// Maps the [0.0, 1.0] value to [steps, 1]
const floored = Math.floor(interp * steps);
const heatIndex = Math.max(1, steps - floored);
return heatIndex;
};
}
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