ssa

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package gopw
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import (
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	"math"
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	"sort"
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)
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// Расчёт процентилей
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// Не работает ;)
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func prctile(input []float64, percent float64) float64 {
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	var percentile float64
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	length := len(input)
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	if length == 0 {
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		return math.NaN()
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	}
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	if length == 1 {
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		return input[0]
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	}
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	if percent <= 0 || percent > 100 {
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		return math.NaN()
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	}
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	// Start by sorting a copy of the slice
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	//c := sortedCopy(input)
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	sort.Float64s(input)
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	// Multiply percent by length of input
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	index := (percent / 100) * float64(len(input))
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	// Check if the index is a whole number
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	if index == float64(int64(index)) {
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		// Convert float to int
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		i := int(index)
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		// Find the value at the index
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		percentile = input[i-1]
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	} else if index > 1 {
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		// Convert float to int via truncation
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		i := int(index)
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		// Find the average of the index and following values
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		// percentile = Mean([]float64{input[i-1], input[i]}) // Mean(Float64Data{input[i-1], input[i]})
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		percentile = (input[i-1] + input[i]) / 2
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	} else {
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		return math.NaN()
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	}
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	return percentile
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}
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// *****************************************************************************
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