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452 lines
9.9 KiB
Markdown
452 lines
9.9 KiB
Markdown
# btree
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[](https://godoc.org/github.com/tidwall/btree)
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An efficient [B-tree](https://en.wikipedia.org/wiki/B-tree) implementation in Go.
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## Features
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- Support for [Generics](#generics) (Go 1.18+).
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- `Map` and `Set` types for ordered key-value maps and sets,
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- Fast bulk loading for pre-ordered data using the `Load()` method.
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- `Copy()` method with copy-on-write support.
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- Thread-safe operations.
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- [Path hinting](PATH_HINT.md) optimization for operations with nearby keys.
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## Using
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To start using this package, install Go and run:
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```sh
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$ go get github.com/tidwall/btree
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```
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## B-tree types
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This package includes the following types of B-trees:
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- [`btree.Map`](#btreemap):
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A fast B-tree for storing ordered key value pairs.
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Go 1.18+
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- [`btree.Set`](#btreeset):
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Like `Map`, but only for storing keys.
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Go 1.18+
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- [`btree.BTreeG`](#btreegeneric):
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A feature-rich B-tree for storing data using a custom comparator.
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Go 1.18+
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- [`btree.BTree`](#btreebtree):
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Like `BTreeG` but uses the `interface{}` type for data. Backwards compatible.
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Go 1.16+
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### btree.Map
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```go
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// Basic
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Set(key, value) // insert or replace an item
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Get(key, value) // get an existing item
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Delete(key) // delete an item
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Len() // return the number of items in the map
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// Iteration
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Scan(iter) // scan items in ascending order
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Reverse(iter) // scan items in descending order
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Ascend(key, iter) // scan items in ascending order that are >= to key
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Descend(key, iter) // scan items in descending order that are <= to key.
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Iter() // returns a read-only iterator for for-loops.
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// Array-like operations
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GetAt(index) // returns the item at index
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DeleteAt(index) // deletes the item at index
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// Bulk-loading
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Load(key, value) // load presorted items into tree
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```
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#### 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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func main() {
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// create a map
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var users btree.Map[string, string]
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// add some users
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users.Set("user:4", "Andrea")
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users.Set("user:6", "Andy")
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users.Set("user:2", "Andy")
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users.Set("user:1", "Jane")
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users.Set("user:5", "Janet")
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users.Set("user:3", "Steve")
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// Iterate over the maps and print each user
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users.Scan(func(key, value string) bool {
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fmt.Printf("%s %s\n", key, value)
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return true
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})
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fmt.Printf("\n")
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// Delete a couple
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users.Delete("user:5")
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users.Delete("user:1")
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// print the map again
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users.Scan(func(key, value string) bool {
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fmt.Printf("%s %s\n", key, value)
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return true
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})
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fmt.Printf("\n")
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// Output:
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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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//
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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:6 Andy
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}
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```
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### btree.Set
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```go
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// Basic
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Insert(key) // insert an item
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Contains(key) // test if item exists
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Delete(key) // delete an item
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Len() // return the number of items in the set
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// Iteration
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Scan(iter) // scan items in ascending order
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Reverse(iter) // scan items in descending order
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Ascend(key, iter) // scan items in ascending order that are >= to key
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Descend(key, iter) // scan items in descending order that are <= to key.
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Iter() // returns a read-only iterator for for-loops.
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// Array-like operations
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GetAt(index) // returns the item at index
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DeleteAt(index) // deletes the item at index
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// Bulk-loading
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Load(key) // load presorted item into tree
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```
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#### 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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func main() {
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// create a set
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var names btree.Set[string]
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// add some names
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names.Insert("Jane")
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names.Insert("Andrea")
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names.Insert("Steve")
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names.Insert("Andy")
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names.Insert("Janet")
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names.Insert("Andy")
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// Iterate over the maps and print each user
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names.Scan(func(key string) bool {
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fmt.Printf("%s\n", key)
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return true
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})
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fmt.Printf("\n")
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// Delete a couple
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names.Delete("Steve")
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names.Delete("Andy")
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// print the map again
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names.Scan(func(key string) bool {
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fmt.Printf("%s\n", key)
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return true
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})
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fmt.Printf("\n")
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// Output:
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// Andrea
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// Andy
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// Jane
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// Janet
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// Steve
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//
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// Andrea
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// Jane
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// Janet
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}
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```
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### btree.BTreeG
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```go
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// Basic
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Set(item) // insert or replace an item
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Get(item) // get an existing item
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Delete(item) // delete an item
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Len() // return the number of items in the btree
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// Iteration
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Scan(iter) // scan items in ascending order
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Reverse(iter) // scan items in descending order
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Ascend(key, iter) // scan items in ascending order that are >= to key
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Descend(key, iter) // scan items in descending order that are <= to key.
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Iter() // returns a read-only iterator for for-loops.
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// Array-like operations
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GetAt(index) // returns the item at index
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DeleteAt(index) // deletes the item at index
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// Bulk-loading
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Load(item) // load presorted items into tree
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// Path hinting
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SetHint(item, *hint) // insert or replace an existing item
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GetHint(item, *hint) // get an existing item
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DeleteHint(item, *hint) // delete an item
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// Copy-on-write
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Copy() // copy the btree
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```
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#### 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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// byKeys is a comparison function that compares item keys and returns true
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// when a is less than b.
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func byKeys(a, b Item) bool {
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return a.Key < b.Key
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}
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// byVals is a comparison function that compares item values and returns true
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// when a is less than b.
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func byVals(a, b Item) bool {
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if a.Val < b.Val {
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return true
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}
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if a.Val > b.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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return byKeys(a, b)
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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.NewBTreeG[Item](byKeys)
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vals := btree.NewBTreeG[Item](byVals)
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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.Set(user)
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vals.Set(user)
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}
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// Iterate over each user in the key tree
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keys.Scan(func(item Item) bool {
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fmt.Printf("%s %s\n", item.Key, item.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.Scan(func(item Item) bool {
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fmt.Printf("%s %s\n", item.Key, item.Val)
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return true
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})
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// Output:
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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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//
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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:5 Janet
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// user:3 Steve
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}
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```
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### btree.BTree
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```go
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// Basic
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Set(item) // insert or replace an item
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Get(item) // get an existing item
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Delete(item) // delete an item
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Len() // return the number of items in the btree
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// Iteration
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Scan(iter) // scan items in ascending order
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Reverse(iter) // scan items in descending order
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Ascend(key, iter) // scan items in ascending order that are >= to key
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Descend(key, iter) // scan items in descending order that are <= to key.
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Iter() // returns a read-only iterator for for-loops.
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// Array-like operations
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GetAt(index) // returns the item at index
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DeleteAt(index) // deletes the item at index
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// Bulk-loading
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Load(item) // load presorted items into tree
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// Path hinting
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SetHint(item, *hint) // insert or replace an existing item
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GetHint(item, *hint) // get an existing item
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DeleteHint(item, *hint) // delete an item
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// Copy-on-write
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Copy() // copy the btree
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```
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#### 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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// byKeys is a comparison function that compares item keys and returns true
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// when a is less than b.
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func byKeys(a, b interface{}) bool {
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i1, i2 := a.(*Item), b.(*Item)
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return i1.Key < i2.Key
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}
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// byVals is a comparison function that compares item values and returns true
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// when a is less than b.
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func byVals(a, b interface{}) bool {
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i1, i2 := a.(*Item), b.(*Item)
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if i1.Val < i2.Val {
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return true
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}
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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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return byKeys(a, b)
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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(byKeys)
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vals := btree.New(byVals)
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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.Set(user)
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vals.Set(user)
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}
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// Iterate over each user in the key tree
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keys.Ascend(nil, func(item interface{}) 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(nil, func(item interface{}) 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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// Output:
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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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//
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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:5 Janet
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// user:3 Steve
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}
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```
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## Performance
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See [tidwall/btree-benchmark](https://github.com/tidwall/btree-benchmark) for benchmark numbers.
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## Contact
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Josh Baker [@tidwall](http://twitter.com/tidwall)
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## License
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Source code is available under the MIT [License](/LICENSE).
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