seqan3::fm_index< alphabet_t, text_layout_mode_, sdsl_index_type_ > Class Template Reference

The SeqAn FM Index. More...

#include <seqan3/search/fm_index/fm_index.hpp>

Inheritance diagram for seqan3::fm_index< alphabet_t, text_layout_mode_, sdsl_index_type_ >:

Public Member Functions
cursor_type	cursor () const noexcept
	Returns a seqan3::fm_index_cursor on the index that can be used for searching. .
bool	empty () const noexcept
	Checks whether the index is empty.
bool	operator!= (fm_index const &rhs) const noexcept
	Compares two indices.
bool	operator== (fm_index const &rhs) const noexcept
	Compares two indices.
size_type	size () const noexcept
	Returns the length of the indexed text including sentinel characters.
Constructors, destructor and assignment
	fm_index ()=default
	Defaulted.
	fm_index (fm_index const &rhs)
	When copy constructing, also update internal data structures.
	fm_index (fm_index &&rhs)
	When move constructing, also update internal data structures.
fm_index &	operator= (fm_index rhs)
	When copy/move assigning, also update internal data structures.
	~fm_index ()=default
	Defaulted.
template<std::ranges::bidirectional_range text_t>
	fm_index (text_t &&text)
	Constructor that immediately constructs the index given a range. The range cannot be empty.

Static Public Attributes
static constexpr text_layout	text_layout_mode = text_layout_mode_
	Indicates whether index is built over a collection.

Friends
template<typename bi_fm_index_t >
class	bi_fm_index_cursor
template<typename fm_index_t >
struct	detail::fm_index_cursor_node
class	detail::reverse_fm_index< alphabet_t, text_layout_mode_, sdsl_index_type_ >
template<typename fm_index_t >
class	fm_index_cursor

Member types
using	alphabet_type = alphabet_t
	The type of the underlying character of the indexed text.
using	size_type = typename sdsl_index_type::size_type
	Type for representing positions in the indexed text.
using	cursor_type = fm_index_cursor< fm_index >
	The type of the (unidirectional) cursor.

Detailed Description

template<semialphabet alphabet_t, text_layout text_layout_mode_, detail::sdsl_index sdsl_index_type_ = default_sdsl_index_type>
class seqan3::fm_index< alphabet_t, text_layout_mode_, sdsl_index_type_ >

The SeqAn FM Index.

Template Parameters

alphabet_t	The alphabet type; must model seqan3::semialphabet.
text_layout_mode_	Indicates whether this index works on a text collection or a single text. See seqan3::text_layout.
sdsl_index_type_	The type of the underlying SDSL index, must model seqan3::sdsl_index.

The seqan3::fm_index is a fast and space-efficient string index to search strings and collections of strings.

General information

Here is a short example on how to build an index and search a pattern using an cursor. Please note that there is a very powerful search module with a high-level interface seqan3::search that encapsulates the use of cursors.

// SPDX-FileCopyrightText: 2006-2025 Knut Reinert & Freie Universität Berlin
// SPDX-FileCopyrightText: 2016-2025 Knut Reinert & MPI für molekulare Genetik
// SPDX-License-Identifier: CC0-1.0
 
#include <vector>
 
#include <seqan3/alphabet/nucleotide/dna4.hpp>
#include <seqan3/core/debug_stream.hpp>
#include <seqan3/search/fm_index/all.hpp>
 
int main()
{
    using namespace seqan3::literals;
 
    std::vector<seqan3::dna4> genome{"ATCGATCGAAGGCTAGCTAGCTAAGGGA"_dna4};
    seqan3::fm_index index{genome}; // build the index
 
    auto cur = index.cursor();                                         // create a cursor
    cur.extend_right("AAGG"_dna4);                                     // search the pattern "AAGG"
    seqan3::debug_stream << "Number of hits: " << cur.count() << '\n'; // outputs: 2
    seqan3::debug_stream << "Positions in the genome: ";
    for (auto && pos : cur.locate()) // outputs: (0, 8), (0, 22)
        seqan3::debug_stream << pos << ' ';
    seqan3::debug_stream << '\n';
    return 0;
}

Attention

When building an index for a single text over any alphabet, the symbol with rank 255 is reserved and may not occur in the text.

Here is an example using a collection of strings (e.g. a genome with multiple chromosomes or a protein database):

// SPDX-FileCopyrightText: 2006-2025 Knut Reinert & Freie Universität Berlin
// SPDX-FileCopyrightText: 2016-2025 Knut Reinert & MPI für molekulare Genetik
// SPDX-License-Identifier: CC0-1.0
 
#include <vector>
 
#include <seqan3/alphabet/nucleotide/dna4.hpp>
#include <seqan3/core/debug_stream.hpp>
#include <seqan3/search/fm_index/all.hpp>
 
int main()
{
    using namespace seqan3::literals;
 
    std::vector<std::vector<seqan3::dna4>> genomes{"ATCTGACGAAGGCTAGCTAGCTAAGGGA"_dna4,
                                                   "TAGCTGAAGCCATTGGCATCTGATCGGACT"_dna4,
                                                   "ACTGAGCTCGTC"_dna4,
                                                   "TGCATGCACCCATCGACTGACTG"_dna4,
                                                   "GTACGTACGTTACG"_dna4};
 
    seqan3::fm_index index{genomes}; // build the index
 
    auto cur = index.cursor();                                         // create a cursor
    cur.extend_right("CTGA"_dna4);                                     // search the pattern "CTGA"
    seqan3::debug_stream << "Number of hits: " << cur.count() << '\n'; // outputs: 5
    seqan3::debug_stream << "Positions in the genomes: ";
    for (auto && pos : cur.locate()) // outputs: (3,16) (2,1) (1,3) (0,2) (1,19)
        seqan3::debug_stream << pos << ' ';
    seqan3::debug_stream << '\n';
    return 0;
}

Attention

When building an index for a text collection over any alphabet, the symbols with rank 254 and 255 are reserved and may not be used in the text.

Constructor & Destructor Documentation

fm_index()

template<semialphabet alphabet_t, text_layout text_layout_mode_, detail::sdsl_index sdsl_index_type_ = default_sdsl_index_type>

template<std::ranges::bidirectional_range text_t>

seqan3::fm_index< alphabet_t, text_layout_mode_, sdsl_index_type_ >::fm_index ( text_t &&  text )

inlineexplicit

Constructor that immediately constructs the index given a range. The range cannot be empty.

Template Parameters

text_t

The type of range to construct from; must model std::ranges::bidirectional_range.

Parameters

[in]

text

The text to construct from.

Complexity

At least linear.

Member Function Documentation

cursor()

template<semialphabet alphabet_t, text_layout text_layout_mode_, detail::sdsl_index sdsl_index_type_ = default_sdsl_index_type>

cursor_type seqan3::fm_index< alphabet_t, text_layout_mode_, sdsl_index_type_ >::cursor ( ) const

inlinenoexcept

Returns a seqan3::fm_index_cursor on the index that can be used for searching. .

Returns

Returns a (unidirectional) seqan3::fm_index_cursor on the index.

Complexity

Constant.

Exceptions

No-throw guarantee.

empty()

template<semialphabet alphabet_t, text_layout text_layout_mode_, detail::sdsl_index sdsl_index_type_ = default_sdsl_index_type>

bool seqan3::fm_index< alphabet_t, text_layout_mode_, sdsl_index_type_ >::empty ( ) const

inlinenoexcept

Checks whether the index is empty.

Returns

true if the index is empty, false otherwise.

Complexity

Constant.

Exceptions

No-throw guarantee.

operator!=()

template<semialphabet alphabet_t, text_layout text_layout_mode_, detail::sdsl_index sdsl_index_type_ = default_sdsl_index_type>

bool seqan3::fm_index< alphabet_t, text_layout_mode_, sdsl_index_type_ >::operator!= ( fm_index< alphabet_t, text_layout_mode_, sdsl_index_type_ > const &  rhs ) const

inlinenoexcept

Compares two indices.

Returns

true if the indices are unequal, false otherwise.

Complexity

Linear.

Exceptions

No-throw guarantee.

operator==()

template<semialphabet alphabet_t, text_layout text_layout_mode_, detail::sdsl_index sdsl_index_type_ = default_sdsl_index_type>

bool seqan3::fm_index< alphabet_t, text_layout_mode_, sdsl_index_type_ >::operator== ( fm_index< alphabet_t, text_layout_mode_, sdsl_index_type_ > const &  rhs ) const

inlinenoexcept

Compares two indices.

Returns

true if the indices are equal, false otherwise.

Complexity

Linear.

Exceptions

No-throw guarantee.

size()

template<semialphabet alphabet_t, text_layout text_layout_mode_, detail::sdsl_index sdsl_index_type_ = default_sdsl_index_type>

size_type seqan3::fm_index< alphabet_t, text_layout_mode_, sdsl_index_type_ >::size ( ) const

inlinenoexcept

Returns the length of the indexed text including sentinel characters.

Returns

Returns the length of the indexed text including sentinel characters.

Complexity

Constant.

Exceptions

No-throw guarantee.

---

The documentation for this class was generated from the following file:

• fm_index.hpp