87 lines
1.8 KiB
Go
87 lines
1.8 KiB
Go
package stats
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import (
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"math"
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)
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// Percentile finds the relative standing in a slice of floats
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func Percentile(input Float64Data, percent float64) (percentile float64, err error) {
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length := input.Len()
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if length == 0 {
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return math.NaN(), EmptyInputErr
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}
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if length == 1 {
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return input[0], nil
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}
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if percent <= 0 || percent > 100 {
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return math.NaN(), BoundsErr
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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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// Multiply percent by length of input
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index := (percent / 100) * float64(len(c))
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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 = c[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(Float64Data{c[i-1], c[i]})
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} else {
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return math.NaN(), BoundsErr
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}
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return percentile, nil
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}
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// PercentileNearestRank finds the relative standing in a slice of floats using the Nearest Rank method
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func PercentileNearestRank(input Float64Data, percent float64) (percentile float64, err error) {
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// Find the length of items in the slice
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il := input.Len()
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// Return an error for empty slices
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if il == 0 {
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return math.NaN(), EmptyInputErr
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}
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// Return error for less than 0 or greater than 100 percentages
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if percent < 0 || percent > 100 {
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return math.NaN(), BoundsErr
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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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// Return the last item
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if percent == 100.0 {
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return c[il-1], nil
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}
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// Find ordinal ranking
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or := int(math.Ceil(float64(il) * percent / 100))
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// Return the item that is in the place of the ordinal rank
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if or == 0 {
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return c[0], nil
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}
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return c[or-1], nil
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}
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