Struct fst::Set
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pub struct Set(_);
Set is a lexicographically ordered set of byte strings.
A Set
is constructed with the SetBuilder
type. Alternatively, a Set
can be constructed in memory from a lexicographically ordered iterator
of byte strings (Set::from_iter
).
A key feature of Set
is that it can be serialized to disk compactly. Its
underlying representation is built such that the Set
can be memory mapped
(Set::from_path
) and searched without necessarily loading the entire
set into memory.
It supports most common operations associated with sets, such as membership, union, intersection, subset/superset, etc. It also supports range queries and automata based searches (e.g. a regular expression).
Sets are represented by a finite state transducer where output values are always zero. As such, sets have the following invariants:
- Once constructed, a
Set
can never be modified. - Sets must be constructed with lexicographically ordered byte sequences.
Methods
impl Set
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fn from_path<P: AsRef<Path>>(path: P) -> Result<Self>
Opens a set stored at the given file path via a memory map.
The set must have been written with a compatible finite state
transducer builder (SetBuilder
qualifies). If the format is invalid
or if there is a mismatch between the API version of this library
and the set, then an error is returned.
fn from_bytes(bytes: Vec<u8>) -> Result<Self>
Creates a set from its representation as a raw byte sequence.
Note that this operation is very cheap (no allocations and no copies).
The set must have been written with a compatible finite state
transducer builder (SetBuilder
qualifies). If the format is invalid
or if there is a mismatch between the API version of this library
and the set, then an error is returned.
fn from_iter<T, I>(iter: I) -> Result<Self> where
T: AsRef<[u8]>,
I: IntoIterator<Item = T>,
T: AsRef<[u8]>,
I: IntoIterator<Item = T>,
Create a Set
from an iterator of lexicographically ordered byte
strings.
If the iterator does not yield values in lexicographic order, then an error is returned.
Note that this is a convenience function to build a set in memory.
To build a set that streams to an arbitrary io::Write
, use
SetBuilder
.
fn contains<K: AsRef<[u8]>>(&self, key: K) -> bool
Tests the membership of a single key.
Example
use fst::Set; let set = Set::from_iter(&["a", "b", "c"]).unwrap(); assert_eq!(set.contains("b"), true); assert_eq!(set.contains("z"), false);
fn stream(&self) -> Stream
Return a lexicographically ordered stream of all keys in this set.
While this is a stream, it does require heap space proportional to the longest key in the set.
If the set is memory mapped, then no further heap space is needed. Note though that your operating system may fill your page cache (which will cause the resident memory usage of the process to go up correspondingly).
Example
Since streams are not iterators, the traditional for
loop cannot be
used. while let
is useful instead:
use fst::{IntoStreamer, Streamer, Set}; let set = Set::from_iter(&["a", "b", "c"]).unwrap(); let mut stream = set.stream(); let mut keys = vec![]; while let Some(key) = stream.next() { keys.push(key.to_vec()); } assert_eq!(keys, vec![b"a", b"b", b"c"]);
fn range(&self) -> StreamBuilder
Return a builder for range queries.
A range query returns a subset of keys in this set in a range given in lexicographic order.
Memory requirements are the same as described on Set::stream
.
Notably, only the keys in the range are read; keys outside the range
are not.
Example
Returns only the keys in the range given.
use fst::{IntoStreamer, Streamer, Set}; let set = Set::from_iter(&["a", "b", "c", "d", "e"]).unwrap(); let mut stream = set.range().ge("b").lt("e").into_stream(); let mut keys = vec![]; while let Some(key) = stream.next() { keys.push(key.to_vec()); } assert_eq!(keys, vec![b"b", b"c", b"d"]);
fn search<A: Automaton>(&self, aut: A) -> StreamBuilder<A>
Executes an automaton on the keys of this set.
Note that this returns a StreamBuilder
, which can be used to
add a range query to the search (see the range
method).
Memory requirements are the same as described on Set::stream
.
Example
An implementation of regular expressions for Automaton
is available
in the fst-regex
crate, which can be used to search sets.
extern crate fst; extern crate fst_regex; use std::error::Error; use fst::{IntoStreamer, Streamer, Set}; use fst_regex::Regex; fn example() -> Result<(), Box<Error>> { let set = Set::from_iter(&[ "foo", "foo1", "foo2", "foo3", "foobar", ]).unwrap(); let re = Regex::new("f[a-z]+3?").unwrap(); let mut stream = set.search(&re).into_stream(); let mut keys = vec![]; while let Some(key) = stream.next() { keys.push(key.to_vec()); } assert_eq!(keys, vec![ "foo".as_bytes(), "foo3".as_bytes(), "foobar".as_bytes(), ]); Ok(()) }
fn len(&self) -> usize
Returns the number of elements in this set.
fn is_empty(&self) -> bool
Returns true if and only if this set is empty.
fn op(&self) -> OpBuilder
Creates a new set operation with this set added to it.
The OpBuilder
type can be used to add additional set streams
and perform set operations like union, intersection, difference and
symmetric difference.
Example
use fst::{IntoStreamer, Streamer, Set}; let set1 = Set::from_iter(&["a", "b", "c"]).unwrap(); let set2 = Set::from_iter(&["a", "y", "z"]).unwrap(); let mut union = set1.op().add(&set2).union(); let mut keys = vec![]; while let Some(key) = union.next() { keys.push(key.to_vec()); } assert_eq!(keys, vec![b"a", b"b", b"c", b"y", b"z"]);
fn is_disjoint<'f, I, S>(&self, stream: I) -> bool where
I: for<'a> IntoStreamer<'a, Into = S, Item = &'a [u8]>,
S: 'f + for<'a> Streamer<'a, Item = &'a [u8]>,
I: for<'a> IntoStreamer<'a, Into = S, Item = &'a [u8]>,
S: 'f + for<'a> Streamer<'a, Item = &'a [u8]>,
Returns true if and only if the self
set is disjoint with the set
stream
.
stream
must be a lexicographically ordered sequence of byte strings.
Example
use fst::{IntoStreamer, Streamer, Set}; let set1 = Set::from_iter(&["a", "b", "c"]).unwrap(); let set2 = Set::from_iter(&["x", "y", "z"]).unwrap(); assert_eq!(set1.is_disjoint(&set2), true); let set3 = Set::from_iter(&["a", "c"]).unwrap(); assert_eq!(set1.is_disjoint(&set3), false);
fn is_subset<'f, I, S>(&self, stream: I) -> bool where
I: for<'a> IntoStreamer<'a, Into = S, Item = &'a [u8]>,
S: 'f + for<'a> Streamer<'a, Item = &'a [u8]>,
I: for<'a> IntoStreamer<'a, Into = S, Item = &'a [u8]>,
S: 'f + for<'a> Streamer<'a, Item = &'a [u8]>,
Returns true if and only if the self
set is a subset of stream
.
stream
must be a lexicographically ordered sequence of byte strings.
Example
use fst::Set; let set1 = Set::from_iter(&["a", "b", "c"]).unwrap(); let set2 = Set::from_iter(&["x", "y", "z"]).unwrap(); assert_eq!(set1.is_subset(&set2), false); let set3 = Set::from_iter(&["a", "c"]).unwrap(); assert_eq!(set1.is_subset(&set3), false); assert_eq!(set3.is_subset(&set1), true);
fn is_superset<'f, I, S>(&self, stream: I) -> bool where
I: for<'a> IntoStreamer<'a, Into = S, Item = &'a [u8]>,
S: 'f + for<'a> Streamer<'a, Item = &'a [u8]>,
I: for<'a> IntoStreamer<'a, Into = S, Item = &'a [u8]>,
S: 'f + for<'a> Streamer<'a, Item = &'a [u8]>,
Returns true if and only if the self
set is a superset of stream
.
stream
must be a lexicographically ordered sequence of byte strings.
Example
use fst::Set; let set1 = Set::from_iter(&["a", "b", "c"]).unwrap(); let set2 = Set::from_iter(&["x", "y", "z"]).unwrap(); assert_eq!(set1.is_superset(&set2), false); let set3 = Set::from_iter(&["a", "c"]).unwrap(); assert_eq!(set1.is_superset(&set3), true); assert_eq!(set3.is_superset(&set1), false);
fn as_fst(&self) -> &Fst
Returns a reference to the underlying raw finite state transducer.
Trait Implementations
impl Debug for Set
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impl AsRef<Fst> for Set
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Returns the underlying finite state transducer.
impl<'s, 'a> IntoStreamer<'a> for &'s Set
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type Item = &'a [u8]
The type of the item emitted by the stream.
type Into = Stream<'s>
The type of the stream to be constructed.
fn into_stream(self) -> Self::Into
Construct a stream from Self
.