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package entropy
import "math"
// Shannon measures the Shannon entropy of a string.
// See http://bearcave.com/misl/misl_tech/wavelets/compression/shannon.html for the algorithmic explanation.
func Shannon(value string) (bits int) {
frq := make(map[rune]float64)
//get frequency of characters
for _, i := range value {
frq[i]++
}
var sum float64
for _, v := range frq {
f := v / float64(len(value))
sum += f * math.Log2(f)
}
bits = int(math.Ceil(sum*-1)) * len(value)
return
}
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