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// Copyright 2019 Google LLC. All Rights Reserved.
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
package ctpolicy
import (
"fmt"
"math/rand"
)
// weightedRandomSample picks an item from the weighted set and returns it.
// Follows weight distribution provided and ignores items whose weight is 0.
// If it's not possible (e.g. all items have 0 weights), returns error.
// Expects all weights to be non-negative, otherwise returns error.
func weightedRandomSample(weights map[string]float32) (string, error) {
var sum float32
for itemName, w := range weights {
if w < 0.0 {
return "", fmt.Errorf("weightedRandomSample got negative weight %v for item %v, all weights should be non-negative", w, itemName)
}
sum += w
}
r := rand.Float32() * sum
for itemName, w := range weights {
if w == 0.0 {
continue
}
r -= w
if r < 0.0 {
return itemName, nil
}
}
return "", fmt.Errorf("weightedRandomSample couldn't pick any item")
}
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