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108 lines
2.4 KiB
Markdown
108 lines
2.4 KiB
Markdown
BTree implementation for Go
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===========================
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[](https://godoc.org/github.com/tidwall/btree)
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This package provides an in-memory B-Tree implementation for Go, useful as
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an ordered, mutable data structure.
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This is a fork of the wonderful [google/btree](https://github.com/google/btree) package. It's has all the same great features and adds a few more.
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- Descend* functions for iterating backwards.
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- Iteration performance boost.
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- User defined context.
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User defined context
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--------------------
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This is a great new feature that allows for entering the same item into multiple B-trees, and each B-tree have a different ordering formula.
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For example:
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```go
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package main
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import (
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"fmt"
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"github.com/tidwall/btree"
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)
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type Item struct {
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Key, Val string
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}
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func (i1 *Item) Less(item btree.Item, ctx interface{}) bool {
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i2 := item.(*Item)
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switch tag := ctx.(type) {
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case string:
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if tag == "vals" {
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if i1.Val < i2.Val {
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return true
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} else if i1.Val > i2.Val {
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return false
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}
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// Both vals are equal so we should fall though
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// and let the key comparison take over.
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}
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}
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return i1.Key < i2.Key
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}
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func main() {
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// Create a tree for keys and a tree for values.
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// The "keys" tree will be sorted on the Keys field.
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// The "values" tree will be sorted on the Values field.
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keys := btree.New(16, "keys")
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vals := btree.New(16, "vals")
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// Create some items.
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users := []*Item{
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&Item{Key: "user:1", Val: "Jane"},
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&Item{Key: "user:2", Val: "Andy"},
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&Item{Key: "user:3", Val: "Steve"},
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&Item{Key: "user:4", Val: "Andrea"},
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&Item{Key: "user:5", Val: "Janet"},
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&Item{Key: "user:6", Val: "Andy"},
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}
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// Insert each user into both trees
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for _, user := range users {
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keys.ReplaceOrInsert(user)
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vals.ReplaceOrInsert(user)
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}
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// Iterate over each user in the key tree
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keys.Ascend(func(item btree.Item) bool {
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kvi := item.(*Item)
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fmt.Printf("%s %s\n", kvi.Key, kvi.Val)
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return true
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})
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fmt.Printf("\n")
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// Iterate over each user in the val tree
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vals.Ascend(func(item btree.Item) bool {
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kvi := item.(*Item)
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fmt.Printf("%s %s\n", kvi.Key, kvi.Val)
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return true
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})
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}
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// Should see the results
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/*
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user:1 Jane
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user:2 Andy
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user:3 Steve
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user:4 Andrea
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user:5 Janet
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user:6 Andy
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user:4 Andrea
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user:2 Andy
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user:6 Andy
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user:1 Jane
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user:3 Steve
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*/
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```
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