예제 #1
0
파일: context.py 프로젝트: dujm/hail
    def import_matrix(self,
                      path,
                      min_partitions=None,
                      drop_samples=False,
                      cell_type=None,
                      missing="NA",
                      has_row_id_name=False):
        """
        :param path: File(s) to read. Currently, takes 1 header line of column ids and subsequent lines of rowID, data... in TSV form where data can be parsed as an integer.
        :type path: str or list of str

        :param min_partitions: Number of partitions.
        :type min_partitions: int or None

        :param bool drop_samples: I don't know if this is relevant, but it only loads the row IDs. Default: False

        :param str cell_type: Tells function how to parse cell data. Can be Int32, Int64, Float32, Float64, or String. Default: Int64

        :param str missing: notation for cell with missing value. Default: "NA"

        :param str has_row_id_name: whether or not the table header has an entry for the Row IDs. Default: False

        :return: Variant dataset imported from file(s)
        :rtype: :py:class:`.VariantDataset`
        """

        if not cell_type:
            cell_type = TInt64()
        return VariantDataset(
            self,
            self._jhc.importMatrices(jindexed_seq_args(path),
                                     joption(min_partitions), drop_samples,
                                     cell_type._jtype, missing,
                                     has_row_id_name))
예제 #2
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    def import_matrix(self,
                      path,
                      key_expr,
                      annotation_types,
                      annotation_headers=None,
                      min_partitions=None,
                      drop_samples=False,
                      cell_type=None,
                      missing="NA"):
        """
        :param path: File(s) to read. Currently, takes 1 header line of column ids and subsequent lines of rowID, data... in TSV form where data can be parsed as an integer.
        :type path: str or list of str

        :param str key_expr: Expression to use for the row key.

        :param annotation_types: List of types to use for the annotation fields. Must be one of: TInt32, TInt64, TFloat32, TFloat64, TString.
        :type min_partitions: list of Type

        :param annotation_headers: List of names to use for the annotation fields. If None, read from file header. Default: None
        :type annotation_headers: list of str or None

        :param min_partitions: Number of partitions.
        :type min_partitions: int or None

        :param bool drop_samples: I don't know if this is relevant, but it only loads the row IDs. Default: False

        :param str cell_type: Tells function how to parse cell data. Can be Int32, Int64, Float32, Float64, or String. Default: Int64

        :param str missing: notation for cell with missing value. Default: "NA"

        :return: Variant dataset imported from file(s)
        :rtype: :py:class:`.VariantDataset`
        """

        if not cell_type:
            cell_type = TInt64()

        if annotation_headers != None and len(annotation_headers) != len(
                annotation_types):
            raise FatalError(
                """annotation_headers and annotation_types have different lengths: 
            each annotation header column must correspond to exactly one annotation type"""
            )

        return VariantDataset(
            self,
            self._jhc.importMatrices(
                jindexed_seq_args(path),
                jsome(jindexed_seq_args(annotation_headers))
                if annotation_headers else jnone(),
                jindexed_seq_args([t._jtype for t in annotation_types]),
                key_expr, joption(min_partitions), drop_samples,
                cell_type._jtype, missing))
예제 #3
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    def read(self, path, drop_samples=False, drop_variants=False):
        """Read .vds file as a variant dataset.

        :param str path: VDS file to read.

        :param bool drop_samples: If True, create sites-only variant
          dataset.  Don't load sample ids, sample annotations
          or gneotypes.

        :param bool drop_variants: If True, create samples-only variant
          dataset (no variants or genotypes).

        :return: Variant dataset read from disk.
        :rtype: :class:`.VariantDataset`

        """

        return VariantDataset(
            self, self._jhc.read(path, drop_samples, drop_variants))
예제 #4
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    def import_vcf(self,
                   path,
                   force=False,
                   force_bgz=False,
                   header_file=None,
                   min_partitions=None,
                   drop_samples=False,
                   call_fields=[],
                   reference_genome=None,
                   contig_recoding=None):
        """Import VCF file(s) as variant dataset.

        **Examples**

        >>> vds = hc1.import_vcf('data/example2.vcf.bgz')

        **Notes**

        Hail is designed to be maximally compatible with files in the `VCF v4.2 spec <https://samtools.github.io/hts-specs/VCFv4.2.pdf>`__.

        :py:meth:`~hail.HailContext.import_vcf` takes a list of VCF files to load. All files must have the same header and the same set of samples in the same order
        (e.g., a variant dataset split by chromosome). Files can be specified as :ref:`Hadoop glob patterns <sec-hadoop-glob>`.

        Ensure that the VCF file is correctly prepared for import: VCFs should either be uncompressed (*.vcf*) or block compressed
        (*.vcf.bgz*).  If you have a large compressed VCF that ends in *.vcf.gz*, it is likely that the file is actually block-compressed,
        and you should rename the file to ".vcf.bgz" accordingly. If you actually have a standard gzipped file, it is possible to import
        it to Hail using the ``force`` optional parameter. However, this is not recommended -- all parsing will have to take place on one node because
        gzip decompression is not parallelizable. In this case, import could take significantly longer.

        If ``generic`` equals False (default), Hail makes certain assumptions about the genotype fields, see :class:`Representation <hail.representation.Genotype>`. On import, Hail filters
        (sets to no-call) any genotype that violates these assumptions. Hail interprets the format fields: GT, AD, OD, DP, GQ, PL; all others are
        silently dropped.

        If ``generic`` equals True, the genotype schema is a :py:class:`~hail.type.TStruct` with field names equal to the IDs of the FORMAT fields.
        The ``GT`` field is automatically read in as a :py:class:`~hail.type.TCall` type. To specify additional fields to import as a
        :py:class:`~hail.type.TCall` type, use the ``call_fields`` parameter. All other fields are imported as the type specified in the FORMAT header field.

        An example genotype schema after importing a VCF with ``generic=True`` is

        .. code-block:: text

            Struct {
                GT: Call,
                AD: Array[Int],
                DP: Int,
                GQ: Int,
                PL: Array[Int]
            }

        .. warning::

            - The variant dataset generated with ``generic=True`` will have significantly slower performance.

            - Not all :py:class:`.VariantDataset` methods will work with a generic genotype schema.

        :py:meth:`~hail.HailContext.import_vcf` does not perform deduplication - if the provided VCF(s) contain multiple records with the same chrom, pos, ref, alt, all
        these records will be imported and will not be collapsed into a single variant.

        Since Hail's genotype representation does not yet support ploidy other than 2,
        this method imports haploid genotypes as diploid. If ``generic=False``, Hail fills in missing indices
        in PL / PP arrays with 1000 to support the standard VCF / VDS "genotype schema.

        Below are two example haploid genotypes and diploid equivalents that Hail sees.

        .. code-block:: text

            Haploid:     1:0,6:7:70:70,0
            Imported as: 1/1:0,6:7:70:70,1000,0

            Haploid:     2:0,0,9:9:24:24,40,0
            Imported as: 2/2:0,0,9:9:24:24,1000,40,1000:1000:0


        .. note::
            
            Using the **FILTER** field:
            
            The information in the FILTER field of a VCF is contained in the ``va.filters`` annotation.
            This annotation is a ``Set`` and can be queried for filter membership with expressions 
            like ``va.filters.contains("VQSRTranche99.5...")``. Variants that are flagged as "PASS" 
            will have no filters applied; for these variants, ``va.filters.isEmpty()`` is true. Thus, 
            filtering to PASS variants can be done with :py:meth:`.VariantDataset.filter_variants_expr`
            as follows:
            
            >>> pass_vds = vds.filter_variants_expr('va.filters.isEmpty()', keep=True)

        **Annotations**

        - **va.filters** (*Set[String]*) -- Set containing all filters applied to a variant. 
        - **va.rsid** (*String*) -- rsID of the variant.
        - **va.qual** (*Double*) -- Floating-point number in the QUAL field.
        - **va.info** (*Struct*) -- All INFO fields defined in the VCF header
          can be found in the struct ``va.info``. Data types match the type
          specified in the VCF header, and if the declared ``Number`` is not
          1, the result will be stored as an array.

        :param path: VCF file(s) to read.
        :type path: str or list of str

        :param bool force: If True, load .gz files serially. This means that no downstream operations
            can be parallelized, so using this mode is strongly discouraged for VCFs larger than a few MB.

        :param bool force_bgz: If True, load .gz files as blocked gzip files (BGZF)

        :param header_file: File to load VCF header from.  If not specified, the first file in path is used.
        :type header_file: str or None

        :param min_partitions: Number of partitions.
        :type min_partitions: int or None

        :param bool drop_samples: If True, create sites-only variant
            dataset.  Don't load sample ids, sample annotations or
            genotypes.

        :param call_fields: FORMAT fields in VCF to treat as a :py:class:`~hail.type.TCall`. Only applies if ``generic=True``.
        :type call_fields: str or list of str

        :param bool generic: If True, read the genotype with a generic schema.
        
        :param reference_genome: Reference genome to use. Default is :class:`~.HailContext.default_reference`.
        :type reference_genome: :class:`.GenomeReference`

        :param contig_recoding: Dict of old contig name to new contig name. The new contig name must be in the reference genome given by ``reference_genome``.
        :type contig_recoding: dict of str to str (or None).

        :return: Variant dataset imported from VCF file(s)
        :rtype: :py:class:`.VariantDataset`

        """

        rg = reference_genome if reference_genome else self.default_reference

        if contig_recoding:
            contig_recoding = TDict(TString(),
                                    TString())._convert_to_j(contig_recoding)

        jvds = self._jhc.importVCFs(jindexed_seq_args(path), force, force_bgz,
                                    joption(header_file),
                                    joption(min_partitions), drop_samples,
                                    jset_args(call_fields), rg._jrep,
                                    joption(contig_recoding))

        return VariantDataset(self, jvds)
예제 #5
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    def import_plink(self,
                     bed,
                     bim,
                     fam,
                     min_partitions=None,
                     delimiter='\\\\s+',
                     missing='NA',
                     quant_pheno=False,
                     a2_reference=True,
                     reference_genome=None,
                     contig_recoding={
                         '23': 'X',
                         '24': 'Y',
                         '25': 'X',
                         '26': 'MT'
                     }):
        """Import PLINK binary file (BED, BIM, FAM) as variant dataset.

        **Examples**

        Import data from a PLINK binary file:

        >>> vds = hc1.import_plink(bed="data/test.bed",
        ...                       bim="data/test.bim",
        ...                       fam="data/test.fam")

        **Notes**

        Only binary SNP-major mode files can be read into Hail. To convert your file from individual-major mode to SNP-major mode, use PLINK to read in your fileset and use the ``--make-bed`` option.

        The centiMorgan position is not currently used in Hail (Column 3 in BIM file).

        The ID (``s``) used by Hail is the individual ID (column 2 in FAM file).

        .. warning::

            No duplicate individual IDs are allowed.

        **Annotations**

        :py:meth:`~hail.HailContext.import_plink` adds the following annotations:

         - **va.rsid** (*String*) -- Column 2 in the BIM file.
         - **sa.famID** (*String*) -- Column 1 in the FAM file. Set to missing if ID equals "0".
         - **sa.patID** (*String*) -- Column 3 in the FAM file. Set to missing if ID equals "0".
         - **sa.matID** (*String*) -- Column 4 in the FAM file. Set to missing if ID equals "0".
         - **sa.isFemale** (*String*) -- Column 5 in the FAM file. Set to missing if value equals "-9", "0", or "N/A".
           Set to true if value equals "2". Set to false if value equals "1".
         - **sa.isCase** (*String*) -- Column 6 in the FAM file. Only present if ``quantpheno`` equals False.
           Set to missing if value equals "-9", "0", "N/A", or the value specified by ``missing``.
           Set to true if value equals "2". Set to false if value equals "1".
         - **sa.qPheno** (*String*) -- Column 6 in the FAM file. Only present if ``quantpheno`` equals True.
           Set to missing if value equals ``missing``.

        :param str bed: PLINK BED file.

        :param str bim: PLINK BIM file.

        :param str fam: PLINK FAM file.

        :param min_partitions: Number of partitions.
        :type min_partitions: int or None

        :param str missing: The string used to denote missing values **only** for the phenotype field. This is in addition to "-9", "0", and "N/A" for case-control phenotypes.

        :param str delimiter: FAM file field delimiter regex.

        :param bool quant_pheno: If True, FAM phenotype is interpreted as quantitative.

        :param bool a2_reference: If True, A2 is treated as the reference allele. If False, A1 is treated as the reference allele.
        
        :param reference_genome: Reference genome to use. Default is :class:`~.HailContext.default_reference`.
        :type reference_genome: :class:`.GenomeReference`
        
        :param contig_recoding: Dict of old contig name to new contig name. The new contig name must be in the reference genome given by ``reference_genome``.
        :type contig_recoding: dict of str to str (or None).        

        :return: Variant dataset imported from PLINK binary file.
        :rtype: :class:`.VariantDataset`
        """

        rg = reference_genome if reference_genome else self.default_reference

        if contig_recoding:
            contig_recoding = TDict(TString(),
                                    TString())._convert_to_j(contig_recoding)

        jvds = self._jhc.importPlink(bed, bim, fam, joption(min_partitions),
                                     delimiter, missing, quant_pheno,
                                     a2_reference, rg._jrep,
                                     joption(contig_recoding))

        return VariantDataset(self, jvds)
예제 #6
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    def import_gen(self,
                   path,
                   sample_file=None,
                   tolerance=0.2,
                   min_partitions=None,
                   chromosome=None,
                   reference_genome=None,
                   contig_recoding=None):
        """Import .gen file(s) as variant dataset.

        **Examples**

        Read a .gen file and a .sample file and write to a .vds file:

        >>> (hc1.import_gen('data/example.gen', sample_file='data/example.sample')
        ...    .write('output/gen_example1.vds'))

        Load multiple files at the same time with :ref:`Hadoop glob patterns <sec-hadoop-glob>`:

        >>> (hc1.import_gen('data/example.chr*.gen', sample_file='data/example.sample')
        ...    .write('output/gen_example2.vds'))

        **Notes**

        For more information on the .gen file format, see `here <http://www.stats.ox.ac.uk/%7Emarchini/software/gwas/file_format.html#mozTocId40300>`__.

        To ensure that the .gen file(s) and .sample file are correctly prepared for import:

        - If there are only 5 columns before the start of the genotype probability data (chromosome field is missing), you must specify the chromosome using the ``chromosome`` parameter

        - No duplicate sample IDs are allowed

        The first column in the .sample file is used as the sample ID ``s``.

        Also, see section in :py:meth:`~hail.HailContext.import_bgen` linked :ref:`here <gpfilters>` for information about Hail's genotype probability representation.

        **Annotations**

        :py:meth:`~hail.HailContext.import_gen` adds the following variant annotations:

         - **va.varid** (*String*) -- 2nd column of .gen file if chromosome present, otherwise 1st column.

         - **va.rsid** (*String*) -- 3rd column of .gen file if chromosome present, otherwise 2nd column.

        :param path: .gen files to import.
        :type path: str or list of str

        :param str sample_file: The sample file.

        :param float tolerance: If the sum of the genotype probabilities for a genotype differ from 1.0 by more than the tolerance, set the genotype to missing.

        :param min_partitions: Number of partitions.
        :type min_partitions: int or None

        :param chromosome: Chromosome if not listed in the .gen file.
        :type chromosome: str or None

        :param reference_genome: Reference genome to use. Default is :class:`~.HailContext.default_reference`.
        :type reference_genome: :class:`.GenomeReference`

        :param contig_recoding: Dict of old contig name to new contig name. The new contig name must be in the reference genome given by ``reference_genome``.
        :type contig_recoding: dict of str to str (or None).

        :return: Variant dataset imported from .gen and .sample files.
        :rtype: :class:`.VariantDataset`
        """

        rg = reference_genome if reference_genome else self.default_reference

        if contig_recoding:
            contig_recoding = TDict(TString(),
                                    TString())._convert_to_j(contig_recoding)

        jvds = self._jhc.importGens(jindexed_seq_args(path), sample_file,
                                    joption(chromosome),
                                    joption(min_partitions), tolerance,
                                    rg._jrep, joption(contig_recoding))
        return VariantDataset(self, jvds)
예제 #7
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    def import_bgen(self,
                    path,
                    tolerance=0.2,
                    sample_file=None,
                    min_partitions=None,
                    reference_genome=None,
                    contig_recoding=None):
        """Import .bgen file(s) as variant dataset.
        
        .. warning::
        
            A BGEN file must have a ``.idx`` file which can be generated by :py:meth:`~hail.HailContext.index_bgen`

        **Examples**

        Importing a BGEN file as a VDS.

        >>> vds = hc1.import_bgen("data/example3.bgen", sample_file="data/example3.sample")

        **Notes**

        Hail supports importing data in the BGEN file format. For more information on the BGEN file format,
        see `here <http://www.well.ox.ac.uk/~gav/bgen_format/bgen_format.html>`__. Note that only v1.1 and v1.2 BGEN files
        are supported at this time. For v1.2 BGEN files, only **unphased** and **diploid** genotype probabilities are allowed and the
        genotype probability blocks must be either compressed with zlib or uncompressed.

        Before importing, ensure that:

          - The sample file has the same number of samples as the BGEN file.
          - No duplicate sample IDs are present.

        To load multiple files at the same time, use :ref:`Hadoop Glob Patterns <sec-hadoop-glob>`.

        .. _gpfilters:

        **Genotype probability (``gp``) representation**:

        The following modifications are made to genotype probabilities in BGEN v1.1 files:

          - Since genotype probabilities are understood to define a probability distribution, :py:meth:`~hail.HailContext.import_bgen` automatically sets to missing those genotypes for which the sum of the probabilities is a distance greater than the ``tolerance`` parameter from 1.0.  The default tolerance is 0.2, so a genotype with sum .79 or 1.21 is filtered out, whereas a genotype with sum .8 or 1.2 remains.

          - :py:meth:`~hail.HailContext.import_bgen` normalizes all probabilities to sum to 1.0. Therefore, an input distribution of (0.98, 0.0, 0.0) will be stored as (1.0, 0.0, 0.0) in Hail.

        **Annotations**

        :py:meth:`~hail.HailContext.import_bgen` adds the following variant annotations:

         - **va.varid** (*String*) -- 2nd column of .gen file if chromosome present, otherwise 1st column.

         - **va.rsid** (*String*) -- 3rd column of .gen file if chromosome present, otherwise 2nd column.

        :param path: .bgen files to import.
        :type path: str or list of str

        :param float tolerance: If the sum of the probabilities for a
            genotype differ from 1.0 by more than the tolerance, set
            the genotype to missing. Only applicable if the BGEN files are v1.1.

        :param sample_file: Sample file.
        :type sample_file: str or None

        :param min_partitions: Number of partitions.
        :type min_partitions: int or None

        :param reference_genome: Reference genome to use. Default is :class:`~.HailContext.default_reference`.
        :type reference_genome: :class:`.GenomeReference`

        :param contig_recoding: Dict of old contig name to new contig name. The new contig name must be in the reference genome given by ``reference_genome``.
        :type contig_recoding: dict of str to str (or None)

        :return: Variant dataset imported from .bgen file.
        :rtype: :class:`.VariantDataset`
        """

        rg = reference_genome if reference_genome else self.default_reference

        if contig_recoding:
            contig_recoding = TDict(TString(),
                                    TString())._convert_to_j(contig_recoding)

        jvds = self._jhc.importBgens(jindexed_seq_args(path),
                                     joption(sample_file), tolerance,
                                     joption(min_partitions), rg._jrep,
                                     joption(contig_recoding))
        return VariantDataset(self, jvds)
예제 #8
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    def balding_nichols_model(self,
                              populations,
                              samples,
                              variants,
                              num_partitions=None,
                              pop_dist=None,
                              fst=None,
                              af_dist=UniformDist(0.1, 0.9),
                              seed=0,
                              reference_genome=None):
        """Simulate a variant dataset using the Balding-Nichols model.

        **Examples**

        To generate a VDS with 3 populations, 100 samples in total, and 1000 variants:

        >>> vds = hc.balding_nichols_model(3, 100, 1000)

        To generate a VDS with 4 populations, 2000 samples, 5000 variants, 10 partitions, population distribution [0.1, 0.2, 0.3, 0.4], :math:`F_{ST}` values [.02, .06, .04, .12], ancestral allele frequencies drawn from a truncated beta distribution with a = .01 and b = .05 over the interval [0.05, 1], and random seed 1:

        >>> from hail.stats import TruncatedBetaDist
        >>> vds = hc.balding_nichols_model(4, 40, 150, 10,
        ...                                pop_dist=[0.1, 0.2, 0.3, 0.4],
        ...                                fst=[.02, .06, .04, .12],
        ...                                af_dist=TruncatedBetaDist(a=0.01, b=2.0, minVal=0.05, maxVal=1.0),
        ...                                seed=1)

        **Notes**

        Hail is able to randomly generate a VDS using the Balding-Nichols model.

        - :math:`K` populations are labeled by integers 0, 1, ..., K - 1
        - :math:`N` samples are named by strings 0, 1, ..., N - 1
        - :math:`M` variants are defined as ``1:1:A:C``, ``1:2:A:C``, ..., ``1:M:A:C``
        - The default ancestral frequency distribution :math:`P_0` is uniform on [0.1, 0.9]. Options are UniformDist(minVal, maxVal), BetaDist(a, b), and TruncatedBetaDist(a, b, minVal, maxVal). All three classes are located in hail.stats.
        - The population distribution :math:`\pi` defaults to uniform
        - The :math:`F_{ST}` values default to 0.1
        - The number of partitions defaults to one partition per million genotypes (i.e., samples * variants / 10^6) or 8, whichever is larger

        The Balding-Nichols model models genotypes of individuals from a structured population comprising :math:`K` homogeneous subpopulations
        that have each diverged from a single ancestral population (a `star phylogeny`). We take :math:`N` samples and :math:`M` bi-allelic variants in perfect
        linkage equilibrium. The relative sizes of the subpopulations are given by a probability vector :math:`\pi`; the ancestral allele frequencies are
        drawn independently from a frequency spectrum :math:`P_0`; the subpopulations have diverged with possibly different :math:`F_{ST}` parameters :math:`F_k`
        (here and below, lowercase indices run over a range bounded by the corresponding uppercase parameter, e.g. :math:`k = 1, \ldots, K`).
        For each variant, the subpopulation allele frequencies are drawn a `beta distribution <https://en.wikipedia.org/wiki/Beta_distribution>`__, a useful continuous approximation of
        the effect of genetic drift. We denote the individual subpopulation memberships by :math:`k_n`, the ancestral allele frequences by :math:`p_{0, m}`,
        the subpopulation allele frequencies by :math:`p_{k, m}`, and the genotypes by :math:`g_{n, m}`. The generative model in then given by:

        .. math::
            k_n \,&\sim\, \pi

            p_{0,m}\,&\sim\, P_0

            p_{k,m}\mid p_{0,m}\,&\sim\, \mathrm{Beta}(\mu = p_{0,m},\, \sigma^2 = F_k p_{0,m}(1 - p_{0,m}))

            g_{n,m}\mid k_n, p_{k, m} \,&\sim\, \mathrm{Binomial}(2, p_{k_n, m})

        We have parametrized the beta distribution by its mean and variance; the usual parameters are :math:`a = (1 - p)(1 - F)/F,\; b = p(1-F)/F` with :math:`F = F_k,\; p = p_{0,m}`.

        **Annotations**

        :py:meth:`~hail.HailContext.balding_nichols_model` adds the following global, sample, and variant annotations:

         - **global.nPops** (*Int*) -- Number of populations
         - **global.nSamples** (*Int*) -- Number of samples
         - **global.nVariants** (*Int*) -- Number of variants
         - **global.popDist** (*Array[Double]*) -- Normalized population distribution indexed by population
         - **global.Fst** (*Array[Double]*) -- :math:`F_{ST}` values indexed by population
         - **global.seed** (*Int*) -- Random seed
         - **global.ancestralAFDist** (*Struct*) -- Description of the ancestral allele frequency distribution
         - **sa.pop** (*Int*) -- Population of sample
         - **va.ancestralAF** (*Double*) -- Ancestral allele frequency
         - **va.AF** (*Array[Double]*) -- Allele frequency indexed by population

        :param int populations: Number of populations.

        :param int samples: Number of samples.

        :param int variants: Number of variants.

        :param int num_partitions: Number of partitions.

        :param pop_dist: Unnormalized population distribution
        :type pop_dist: array of float or None

        :param fst: :math:`F_{ST}` values
        :type fst: array of float or None

        :param af_dist: Ancestral allele frequency distribution
        :type af_dist: :class:`.UniformDist` or :class:`.BetaDist` or :class:`.TruncatedBetaDist`

        :param int seed: Random seed.

        :param reference_genome: Reference genome to use. Default is :class:`~.HailContext.default_reference`.
        :type reference_genome: :class:`.GenomeReference`

        :return: Variant dataset simulated using the Balding-Nichols model.
        :rtype: :class:`.VariantDataset`
        """

        if pop_dist is None:
            jvm_pop_dist_opt = joption(pop_dist)
        else:
            jvm_pop_dist_opt = joption(jarray(self._jvm.double, pop_dist))

        if fst is None:
            jvm_fst_opt = joption(fst)
        else:
            jvm_fst_opt = joption(jarray(self._jvm.double, fst))

        rg = reference_genome if reference_genome else self.default_reference

        jvds = self._jhc.baldingNicholsModel(populations, samples, variants,
                                             joption(num_partitions),
                                             jvm_pop_dist_opt, jvm_fst_opt,
                                             af_dist._jrep(), seed, rg._jrep)
        return VariantDataset(self, jvds)