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package main
import (
"math/rand"
"sort"
)
// combinations takes input in the form of a map of item lists, and returns a
// list of all combinations of each item for each key. E.g.:
//
// {"foo": [1, 2, 3], "bar": [4, 5, 6]}
//
// Will return the following maps:
//
// {"foo": 1, "bar": 4}
// {"foo": 1, "bar": 5}
// {"foo": 1, "bar": 6}
// {"foo": 2, "bar": 4}
// {"foo": 2, "bar": 5}
// {"foo": 2, "bar": 6}
// {"foo": 3, "bar": 4}
// {"foo": 3, "bar": 5}
// {"foo": 3, "bar": 6}
func combinations(items map[string][]interface{}) []map[string]interface{} {
keys := []string{}
for key := range items {
keys = append(keys, key)
}
sort.Strings(keys)
return combiner(map[string]interface{}{}, keys, items)
}
// combiner is a utility function for combinations.
func combiner(head map[string]interface{}, pending []string, items map[string][]interface{}) []map[string]interface{} {
if len(pending) == 0 {
return []map[string]interface{}{head}
}
key, pending := pending[0], pending[1:]
result := []map[string]interface{}{}
for _, value := range items[key] {
path := map[string]interface{}{}
for k, v := range head {
path[k] = v
}
path[key] = value
result = append(result, combiner(path, pending, items)...)
}
return result
}
// uniformChoice chooses a single random item from the argument list, uniformly weighted.
type uniformChoice []interface{}
func (uc uniformChoice) Choose(r *rand.Rand) interface{} {
return uc[r.Intn(len(uc))]
}
// probSetChoice picks a set of strings based on each string's probability (0-1).
type probSetChoice map[string]float64
func (pc probSetChoice) Choose(r *rand.Rand) []string {
choices := []string{}
for item, prob := range pc {
if r.Float64() <= prob {
choices = append(choices, item)
}
}
return choices
}
// uniformSetChoice picks a set of strings with uniform probability, picking at least one.
type uniformSetChoice []string
func (usc uniformSetChoice) Choose(r *rand.Rand) []string {
choices := []string{}
indexes := r.Perm(len(usc))
if len(indexes) > 1 {
indexes = indexes[:1+r.Intn(len(indexes)-1)]
}
for _, i := range indexes {
choices = append(choices, usc[i])
}
return choices
}