radixtree

README

radixtree

Package radixtree implements an Adaptive Radix Tree, aka compressed trie or compact prefix tree. This data structure is useful to quickly lookup data by key, find values whose keys have a common prefix, or find values whose keys are a prefix (i.e. found along the way) of a search key.

It is adaptive in the sense that nodes are not constant size, having only as many children, up to the maximum, as needed to branch to all subtrees. This package implements a radix-256 tree where each key symbol (radix) is a byte, allowing up to 256 possible branches to traverse to the next node.

The implementation is optimized for read performance and does not allocate heap memory for read operation (Get, Iter, IterPath, etc.). Once a radix tree is built, it can be repeatedly searched quickly. Concurrent searches are safe since these do not modify the data structure. Access is not synchronized (not concurrent safe with writes), allowing the caller to synchronize, if needed, in whatever manner works best for the application.

This radix tree offers the following features:

• Efficient: Operations are O(key-len). Zero memory allocation for reading items or iteration.
• Ordered iteration: Iterating the tree is done in lexical order, making the output deterministic.
• Store nil values: Read operations differentiate between missing and nil values.
• Compact: When values are stored using keys that have a common prefix, the common part of the key is only stored once. Consider this when keys are similar to a timestamp, OID, filepath, geohash, network address, etc. Only the minimum number of nodes are kept to branch at the points where keys differ.
• Iterators: Go 1.23 iterators allow ranging over key-value pairs stored in the tree. Iterators can traverse all key-value pairs, pairs with a key having specified prefix, or pairs along a key-path from root to a specified key.
• A Stepper type of iterator traverses the tree one specified byte at a time, and is useful for incremental lookup. A Stepper can be copied in order to branch a search and iterate the copies concurrently.
• Generics: The tree stores the specified type of value without needing to do interface type assertion.

Install

$ go get github.com/gammazero/radixtree

Example

package main

import (
    "fmt"
    "github.com/gammazero/radixtree"
)

func main() {
    rt := radixtree.New()
    rt.Put("tomato", "TOMATO")
    rt.Put("tom", "TOM")
    rt.Put("tommy", "TOMMY")
    rt.Put("tornado", "TORNADO")

    val, found := rt.Get("tom")
    if found {
        fmt.Println("Found", val)
    }
    // Output: Found TOM

    // Find all items whose keys start with "tom".
    for key, value := range rt.IterAt("tom") {
        fmt.Println(key, "=", value)
    }
    // Output:
    // tom = TOM
    // tomato = TOMATO
    // tommy = TOMMY

    // Find all items whose keys are a prefix of "tomato"
    for _, value := range rt.IterPath("tomato") {
        fmt.Println(value)
    }
    // Output:
    // TOM
    // TOMATO

    if rt.Delete("tom") {
        fmt.Println("Deleted tom")
    }
    // Output: Deleted tom

    val, found = rt.Get("tom")
    if found {
        fmt.Println("Found", val)
    } else {
        fmt.Println("not found")
    }
    // Output: not found
}

License

MIT License

Documentation

Overview

Package radixtree implements an Adaptive Radix Tree, aka compressed trie or compact prefix tree. It is adaptive in the sense that nodes are not constant size, having as few or many children as needed to branch to all subtrees.

This package implements a radix-256 tree where each key symbol (radix) is a byte, allowing up to 256 possible branches to traverse to the next node.

The implementation is optimized for read performance and allocates zero bytes of heap memory for read oprations. Once the radix tree is built, it can be repeatedly searched quickly. Concurrent searches are safe since these do not modify the radixtree. Access is not synchronized (not concurrent safe with writes), allowing the caller to synchronize, if needed, in whatever manner works best for the application.

The API uses string keys, since strings are immutable and therefore it is not necessary make a copy of the key provided to the radix tree.

Index

• type InspectFunc
• type Item
  • func (kv *Item[T]) Key() string
  • func (kv *Item[T]) Value() T
• type Stepper
  • func (s *Stepper[T]) Copy() *Stepper[T]
  • func (s *Stepper[T]) Item() *Item[T]
  • func (s *Stepper[T]) Next(radix byte) bool
  • func (s *Stepper[T]) Value() (T, bool)
• type Tree
  • func New[T any]() *Tree[T]
  • func (t *Tree[T]) Delete(key string) bool
  • func (t *Tree[T]) DeletePrefix(prefix string) bool
  • func (t *Tree[T]) Get(key string) (T, bool)
  • func (t *Tree[T]) Inspect(inspectFn InspectFunc[T])
  • func (t *Tree[T]) Iter() iter.Seq2[string, T]
  • func (t *Tree[T]) IterAt(key string) iter.Seq2[string, T]
  • func (t *Tree[T]) IterPath(key string) iter.Seq2[string, T]
  • func (t *Tree[T]) Len() int
  • func (t *Tree[T]) NewStepper() *Stepper[T]
  • func (t *Tree[T]) Put(key string, value T) bool

Examples

• Tree.Iter
• Tree.IterAt
• Tree.IterPath
• Tree.NewStepper

Types

type InspectFunc

type InspectFunc[T any] func(link, prefix, key string, depth, children int, hasValue bool, value T) bool

InspectFunc is the type of the function called for each node visited by Inspect. The key argument contains the key at which the node is located, the depth is the distance from the root of the tree, and children is the number of children the node has.

If the function returns true Inspect stops immediately and returns.

type Item

type Item[T any] struct {
	// contains filtered or unexported fields
}

func (*Item[T]) Key

func (kv *Item[T]) Key() string

func (*Item[T]) Value

func (kv *Item[T]) Value() T

type Stepper

type Stepper[T any] struct {
	// contains filtered or unexported fields
}

Stepper traverses a Tree one byte at a time.

Any modification to the tree invalidates the Stepper.

func (*Stepper[T]) Copy

func (s *Stepper[T]) Copy() *Stepper[T]

Copy makes a copy of the current Stepper. This allows branching a Stepper into two that can take separate paths. These Steppers do not affect each other and can be used concurrently.

func (*Stepper[T]) Item

func (s *Stepper[T]) Item() *Item[T]

Item returns an Item containing the key and value at the current Stepper position, or returns nil if no value is present at the position.

func (*Stepper[T]) Next

func (s *Stepper[T]) Next(radix byte) bool

Next advances the Stepper from its current position, to the position of given key symbol in the tree, so long as the given symbol is next in a path in the tree. If the symbol allows the Stepper to advance, then true is returned. Otherwise false is returned.

When false is returned the Stepper is not modified. This allows different values to be used in subsequent calls to Next.

func (*Stepper[T]) Value

func (s *Stepper[T]) Value() (T, bool)

Value returns the value at the current Stepper position, and true or false to indicate if a value is present at the position.

type Tree

type Tree[T any] struct {
	// contains filtered or unexported fields
}

Tree is a radix tree of bytes keys and any values.

func New

func New[T any]() *Tree[T]

New creates a new bytes-based radix tree

func (*Tree[T]) Delete

func (t *Tree[T]) Delete(key string) bool

Delete removes the value associated with the given key. Returns true if there was a value stored for the key. If the node or any of its ancestors becomes childless as a result, they are removed from the tree.

func (*Tree[T]) DeletePrefix

func (t *Tree[T]) DeletePrefix(prefix string) bool

DeletePrefix removes all values whose key is prefixed by the given prefix. Returns true if any values were removed.

func (*Tree[T]) Get

func (t *Tree[T]) Get(key string) (T, bool)

Get returns the value stored at the given key. Returns false if there is no value present for the key.

func (*Tree[T]) Inspect

func (t *Tree[T]) Inspect(inspectFn InspectFunc[T])

Inspect walks every node of the tree, whether or not it holds a value, calling inspectFn with information about each node. This allows the structure of the tree to be examined and detailed statistics to be collected.

If inspectFn returns false, the traversal is stopped and Inspect returns.

The tree is traversed in lexical order, making the output deterministic.

func (*Tree[T]) Iter

func (t *Tree[T]) Iter() iter.Seq2[string, T]

Iter visits all nodes in the tree, yielding the key and value of each.

The tree is traversed in lexical order, making the output deterministic.

Example

package main

import (
	"fmt"

	"github.com/gammazero/radixtree"
)

func main() {
	rt := radixtree.New[int]()
	rt.Put("mercury", 1)
	rt.Put("venus", 2)
	rt.Put("earth", 3)
	rt.Put("mars", 4)

	// Find all items that that have a key that is a prefix of "tomato".
	for key, value := range rt.Iter() {
		fmt.Println(key, "=", value)
	}
}

Output:

earth = 3
mars = 4
mercury = 1
venus = 2

func (*Tree[T]) IterAt

func (t *Tree[T]) IterAt(key string) iter.Seq2[string, T]

IterAt visits all nodes whose keys match or are prefixed by the specified key, yielding the key and value of each. An empty key "" to visits all nodes, and is the same as calling Iter.

The tree is traversed in lexical order, making the output deterministic.

Example

package main

import (
	"fmt"

	"github.com/gammazero/radixtree"
)

func main() {
	rt := radixtree.New[string]()
	rt.Put("tomato", "TOMATO")
	rt.Put("tom", "TOM")
	rt.Put("tommy", "TOMMY")
	rt.Put("tornado", "TORNADO")

	// Find all items whose keys start with "tom".
	for _, value := range rt.IterAt("tom") {
		fmt.Println(value)
	}
}

Output:

TOM
TOMATO
TOMMY

func (*Tree[T]) IterPath

func (t *Tree[T]) IterPath(key string) iter.Seq2[string, T]

IterPath returns an iterator that visits each node along the path from the root to the node at the given key. yielding the key and value of each.

The tree is traversed in lexical order, making the output deterministic.

Example

package main

import (
	"fmt"

	"github.com/gammazero/radixtree"
)

func main() {
	rt := radixtree.New[string]()
	rt.Put("tomato", "TOMATO")
	rt.Put("tom", "TOM")
	rt.Put("tommy", "TOMMY")
	rt.Put("tornado", "TORNADO")

	// Find all items that that have a key that is a prefix of "tomato".
	for key, value := range rt.IterPath("tomato") {
		fmt.Println(key, "=", value)
	}
}

Output:

tom = TOM
tomato = TOMATO

func (*Tree[T]) Len

func (t *Tree[T]) Len() int

Len returns the number of values stored in the tree.

func (*Tree[T]) NewStepper

func (t *Tree[T]) NewStepper() *Stepper[T]

NewStepper returns a new Stepper instance that begins at the root of the tree.

Example

package main

import (
	"fmt"

	"github.com/gammazero/radixtree"
)

func main() {
	rt := radixtree.New[string]()
	rt.Put("tomato", "TOMATO")
	rt.Put("tom", "TOM")
	rt.Put("tommy", "TOMMY")
	rt.Put("tornado", "TORNADO")

	stepper := rt.NewStepper()
	word := "tomato"
	for i := range word {
		if !stepper.Next(word[i]) {
			break
		}
		if val, ok := stepper.Value(); ok {
			fmt.Println(val)
		}
	}
}

Output:

TOM
TOMATO

func (*Tree[T]) Put

func (t *Tree[T]) Put(key string, value T) bool

Put inserts the value into the tree at the given key, replacing any existing items. It returns true if it adds a new value, false if it replaces an existing value.