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. Cursor is pointing to the root node of the implicit suffix tree. .

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.

template<cereal_archive archive_t>
void	serialize (archive_t &archive)
	Serialisation support function.

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.

Private Member Functions
template<std::ranges::range text_t> requires (text_layout_mode_ == text_layout::single)
void	construct (text_t &&text)
	Constructs the index given a range. The range cannot be an rvalue (i.e. a temporary object) and has to be non-empty.

template<std::ranges::range text_t> requires (text_layout_mode_ == text_layout::collection)
void	construct (text_t &&text, bool reverse=false)
	This is an overloaded member function, provided for convenience. It differs from the above function only in what argument(s) it accepts.

Static Private Member Functions
template<typename output_it_t , typename sequence_t >
static output_it_t	copy_sequence_ranks_shifted_by_one (output_it_t output_it, sequence_t &&sequence)
	Eagerly convert sequence into ranks, shift by one and copy them into output_it.

Private Attributes
sdsl_index_type	index
	Underlying index from the SDSL.

seqan3::contrib::sdsl::sd_vector	text_begin
	Bitvector storing begin positions for collections.

seqan3::contrib::sdsl::rank_support_sd< 1 >	text_begin_rs
	Rank support for text_begin.

seqan3::contrib::sdsl::select_support_sd< 1 >	text_begin_ss
	Select support for text_begin.

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	sdsl_index_type = sdsl_index_type_
	The type of the underlying SDSL index.

using	sdsl_char_type = typename sdsl_index_type::alphabet_type::char_type
	The type of the reduced alphabet type. (The reduced alphabet might be smaller than the original alphabet in case not all possible characters occur in the indexed text.)

using	sdsl_sigma_type = typename sdsl_index_type::alphabet_type::sigma_type
	The type of the alphabet size of the underlying SDSL index.

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.

Choosing an index implementation

The underlying implementation of the FM Index (rank data structure, sampling rates, etc.) can be specified by passing a new SDSL index type as second template parameter:

Todo:: Link to SDSL documentation or write our own once SDSL3 documentation is available somewhere....

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

Todo:: At least linear.

Member Function Documentation

◆ construct()

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

template<std::ranges::range text_t>
requires (text_layout_mode_ == text_layout::single)

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

inlineprivate

Constructs the index given a range. The range cannot be an rvalue (i.e. a temporary object) and has to be non-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.

Todo:: This has to be better implemented with regard to the memory peak due to not matching interfaces with the SDSL.

Complexity

Todo:: At least linear.

Exceptions

No guarantee.

Todo:: Ensure strong exception guarantee.

◆ 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. Cursor is pointing to the root node of the implicit suffix tree. .

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.

◆ serialize()

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

template<cereal_archive archive_t>

void seqan3::fm_index< alphabet_t, text_layout_mode_, sdsl_index_type_ >::serialize ( archive_t & archive )

inline

Serialisation support function.

Template Parameters

archive_t Type of archive; must satisfy seqan3::cereal_archive.

Parameters

archive The archive being serialised from/to.

Attention: These functions are never called directly, see Serialisation for more details.

◆ 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

Public Member Functions

Static Public Attributes

Private Member Functions

Static Private Member Functions

Private Attributes

Friends

Member types

Detailed Description

General information

Choosing an index implementation

Constructor & Destructor Documentation

◆ fm_index()

Complexity

Member Function Documentation

◆ construct()

Complexity

Exceptions

◆ cursor()

Complexity

Exceptions

◆ empty()

Complexity

Exceptions

◆ operator!=()

Complexity

Exceptions

◆ operator==()

Complexity

Exceptions

◆ serialize()

◆ size()

Complexity

Exceptions