66 lines
1.7 KiB
Go
66 lines
1.7 KiB
Go
package main
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import (
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"fmt"
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"math"
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)
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func mean(v []float64) (m float64, ok bool) {
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if len(v) == 0 {
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return
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}
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// an algorithm that attempts to retain accuracy
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// with widely different values.
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var parts []float64
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for _, x := range v {
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var i int
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for _, p := range parts {
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sum := p + x
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var err float64
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switch ax, ap := math.Abs(x), math.Abs(p); {
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case ax < ap:
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err = x - (sum - p)
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case ap < ax:
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err = p - (sum - x)
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}
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if err != 0 {
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parts[i] = err
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i++
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}
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x = sum
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}
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parts = append(parts[:i], x)
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}
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var sum float64
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for _, x := range parts {
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sum += x
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}
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return sum / float64(len(v)), true
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}
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func main() {
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for _, v := range [][]float64{
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[]float64{}, // mean returns ok = false
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[]float64{math.Inf(1), math.Inf(1)}, // answer is +Inf
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// answer is NaN, and mean returns ok = true, indicating NaN
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// is the correct result
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[]float64{math.Inf(1), math.Inf(-1)},
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[]float64{3, 1, 4, 1, 5, 9},
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// large magnitude numbers cancel. answer is mean of small numbers.
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[]float64{1e20, 3, 1, 4, 1, 5, 9, -1e20},
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[]float64{10, 9, 8, 7, 6, 5, 4, 3, 2, 1, 0, 0, 0, 0, .11},
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[]float64{10, 20, 30, 40, 50, -100, 4.7, -11e2},
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} {
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fmt.Println("Vector:", v)
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if m, ok := mean(v); ok {
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fmt.Printf("Mean of %d numbers is %g\n\n", len(v), m)
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} else {
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fmt.Println("Mean undefined\n")
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}
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}
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}
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