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ergo/vendor/github.com/tidwall/btree/README.md
2020-02-12 13:19:23 -05:00

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