71 lines
1.7 KiB
Go
71 lines
1.7 KiB
Go
package random
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import (
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"errors"
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"slices"
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)
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// WeightedChooser allows to randomly choose an entry based on their weights
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// (higher weight = higher chance of being chosen). Based on the subtraction method described in
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// https://eli.thegreenplace.net/2010/01/22/weighted-random-generation-in-python/
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type WeightedChooser[T any] struct {
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entries []T
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weights []int
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totalWeight int
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}
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func NewWeightedChooser[T any]() *WeightedChooser[T] {
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return &WeightedChooser[T]{}
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}
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func (w *WeightedChooser[T]) Add(value T, weight int) {
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w.entries = append(w.entries, value)
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w.weights = append(w.weights, weight)
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w.totalWeight += weight
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}
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// Pick choose a random entry based on their weights, and removes it from the list
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func (w *WeightedChooser[T]) Pick() (T, error) {
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var empty T
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if w.totalWeight == 0 {
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return empty, errors.New("cannot choose from zero weight")
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}
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i, err := w.weightedChoice()
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if err != nil {
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return empty, err
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}
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entry := w.entries[i]
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_ = w.Remove(i)
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return entry, nil
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}
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func (w *WeightedChooser[T]) weightedChoice() (int, error) {
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if len(w.entries) == 0 {
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return 0, errors.New("cannot choose from empty list")
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}
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rnd := Int64N(w.totalWeight)
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for i, weight := range w.weights {
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rnd -= int64(weight)
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if rnd < 0 {
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return i, nil
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}
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}
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return 0, errors.New("internal error - code should not reach this point")
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}
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func (w *WeightedChooser[T]) Remove(i int) error {
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if i < 0 || i >= len(w.entries) {
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return errors.New("index out of bounds")
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}
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w.totalWeight -= w.weights[i]
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w.weights = slices.Delete(w.weights, i, i+1)
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w.entries = slices.Delete(w.entries, i, i+1)
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return nil
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}
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func (w *WeightedChooser[T]) Size() int {
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return len(w.entries)
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}
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