50 lines
857 B
Go
50 lines
857 B
Go
// For more tutorials: https://blog.learngoprogramming.com
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//
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// Copyright © 2018 Inanc Gumus
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// Learn Go Programming Course
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// License: https://creativecommons.org/licenses/by-nc-sa/4.0/
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//
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package main
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import (
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"sort"
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)
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type group struct {
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sum map[string]record // metrics per group key
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keys []string // unique group keys
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key groupFunc
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}
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func groupBy(key groupFunc) *group {
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return &group{
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sum: make(map[string]record),
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key: key,
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}
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}
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// digest the records
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func (g *group) digest(records iterator) error {
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return records.each(func(r record) {
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k := g.key(r)
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if _, ok := g.sum[k]; !ok {
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g.keys = append(g.keys, k)
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}
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g.sum[k] = r.sum(g.sum[k])
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})
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}
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// each yields the grouped records
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func (g *group) each(yield recordFn) error {
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sort.Strings(g.keys)
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for _, k := range g.keys {
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yield(g.sum[k])
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}
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return nil
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}
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