# Source code for egglib.stats._ld

```
"""
Copyright 2015-2021 Stephane De Mita, Mathieu Siol
This file is part of EggLib.
EggLib is free software: you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation, either version 3 of the License, or
(at your option) any later version.
EggLib is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.
You should have received a copy of the GNU General Public License
along with EggLib. If not, see <http://www.gnu.org/licenses/>.
"""
from .. import eggwrapper as _eggwrapper
from .. import _interface
from .. import _site
def _get_stats(pld, multiple_policy, min_freq):
if pld.num_alleles1() > 2 or pld.num_alleles2() > 2:
if multiple_policy == 'forbid':
raise ValueError('at least one locus has more than two alleles and this is not allowed')
elif multiple_policy == 'main':
freq1 = [pld.freq1(i) for i in range(pld.num_alleles1())]
freq2 = [pld.freq2(i) for i in range(pld.num_alleles2())]
a1 = [freq1.index(max(freq1))]
a2 = [freq2.index(max(freq2))]
elif multiple_policy == 'average':
a1 = [i for i in range(pld.num_alleles1()) if pld.freq1(i) >= min_freq]
a2 = [i for i in range(pld.num_alleles2()) if pld.freq2(i) >= min_freq]
else:
raise ValueError('invalid value for `multiple_policy` option: {0}'.format(multiple_policy))
else:
a1 = [0]
a2 = [0]
n = 0
D = 0.0
Dp = 0.0
r = 0.0
rsq = 0.0
for i in a1:
for j in a2:
n += 1
pld.compute(i, j)
D += pld.D()
Dp += pld.Dp()
r += pld.r()
rsq += pld.rsq()
if n == 0:
return {'D': None, 'Dp': None, 'r': None, 'rsq': None}
if n > 1:
D /= n
Dp /= n
r /= n
rsq /= n
return {'D': D, 'Dp': Dp, 'r': r, 'rsq': rsq, 'n': n}
[docs]def pairwise_LD(locus1, locus2, struct=None, multiple_policy='main', min_freq=0):
"""
Linkage disequilibium between a pair of loci.
:class:`.Site` instances must be used to describe loci. Only the order of
samples is considered and both loci must have the same number of
samples.
:param locus1: A :class:`.Site` instance.
:param locus2: A :class:`.Site` instance.
:param struct: A :class:`.Structure` object used to describe the
individual level. If specified, genotypes are automatically
described and genotypic linkage is processed. By default, consider
all samples as originating from haploid individuals.
:param multiple_policy: Determine what is done if either input locus
has more than two alleles. Possible values are, ``"forbid"``
(raise an exception if this occurs), ``"main"`` (take
the most frequent allele of each locus) and ``"average"`` (
compute the unweighted average over all possible pair of
alleles). More options might be added in future versions. This
option is ignored if both loci have less than three alleles. If
``"main"`` and there are several equally most frequent alleles,
the first-occurring one is used (arbitrarily).
:param min_freq: Only used if at least one site has more than two
alleles and *multiple_policy* is set to *average*. Set the
minimum absolute frequency to consider an allele.
:return: A dictionary of linkage disequilibrium statistics. In case
statistics cannot be computed (either site fixed, or less than
two samples with non-missing data at both sites), computed
values are replaced by ``None``. ``n`` gives the number of pairs
of alleles considered (0 if statistics are not computed at all).
"""
if locus1.ns != locus2.ns: raise ValueError('the number of samples must match in the two loci')
if locus1.ns < 2: raise ValueError('the number of samples must be at least 2')
if struct is None:
struct = _eggwrapper.StructureHolder()
struct.mk_dummy_structure(locus1.ns, 1)
struct2 = struct
else:
if struct.req_ns > locus1.ns: raise ValueError('mismatch with structure')
if struct.req_no > locus1.ns: raise ValueError('mismatch with structure')
struct2 = struct.make_auxiliary()._obj
struct = struct._obj
site1 = _eggwrapper.Genotypes()
site2 = _eggwrapper.Genotypes()
site1.process(locus1._obj, struct)
site2.process(locus2._obj, struct)
frq1 = _eggwrapper.FreqHolder()
frq1.setup_structure(struct2)
frq1.process_site(site1.site())
frq2 = _eggwrapper.FreqHolder()
frq2.setup_structure(struct2)
frq2.process_site(site2.site())
ld = _eggwrapper.PairwiseLD()
if not ld.process(site1.site(), site2.site(), frq1, frq2, struct2, 0, 1.0):
return {'D': None, 'Dp': None, 'r': None, 'rsq': None, 'n': 0}
return _get_stats(ld, multiple_policy, min_freq)
[docs]def matrix_LD(align, stats, struct=None, multiple_policy='main',
min_freq=0, min_n=2, max_maj=1.0, positions=None):
"""
Linkage disequilibrium statistics between all
pairs of sites. The computed statistics
are selected by an argument of this function. Return a matrix (as a
nested :class:`list`) of the requested statistics. In all cases, all
pairs of sites are present in the returned matrices. If statistics
cannot be computed, they are replaced by :data:`None`.
The available statistics are:
* ``d`` -- Distance between sites of the pairs.
* ``D`` -- Standard linkage disequilibrium.
* ``Dp`` -- Lewontin's D'.
* ``r`` -- Correlation coefficient.
* ``rsq`` -- Equivalent to r\ :sup:`2`.
:param align: An :class:`.Align` instance.
:param stats: Requested statistic or statistics (see list of
available statistics above, as a single string or as a list of
one or more of these statistics (in any order).
:param struct: A :class:`.Structure` object used to describe the
individual level. If specified, genotypes are automatically
described and genotypic linkage is processed. By default, consider
all samples as originating from haploid individuals.
:param multiple_policy: Specify what is done for pairs of sites for
which at least one locus has only one allele. See
:func:`pairwise_LD` for further description.
:param min_freq: Only used if at least one site has more than two
alleles and depending on the value of *multiple_policy*. See
:func:`pairwise_LD` for further description.
:param min_n: Minimum number of samples used (this value must
always be larger than 1). Sites not fulfilling this criterion
will be dropped.
:param max_maj: Maximum relative frequency of the majority allele.
Sites not fulfilling this criterion will be dropped.
:param positions: A sequence of positions, whose length must match
the number of sites of the provided alignment. Used in the
return value to describe the used sites, and, if requested, to
compute the distance between sites. By default, the position of
sites in the original alignment is used.
:return: Returns a tuple with two items: first is the list of
positions of sites used in the matrix (a subset of the sites of
the provided alignment), with positions provided by the
corresponding argument (by default, the index of sites); second
is the matrix, as the nested lower half matrix. The matrix
contains items for all i and j indexes with 0 <= j <= i < n
where n is the number of retained sites. The content of the
matrix is represented by a single value (if a single statistic
has been requested) or as a list of 1 or more values (if a list
of 1 or more, accordingly, statistics have been requested), or
``None`` for the diagonal or if the pairwise comparison was
dropped for any reason.
"""
# initialize local variables
mLD = _eggwrapper.MatrixLD()
retained = []
if struct is None:
struct = _eggwrapper.StructureHolder()
struct.mk_dummy_structure(align.ns, 1)
else:
struct = struct._obj
mLD.set_structure(struct)
# check arguments
min_n = int(min_n)
if min_n < 2: raise ValueError('too small value for `min_n` argument: {0}'.format(min_n))
max_maj = float(max_maj)
if max_maj < 0.5 or max_maj > 1.0: raise ValueError('invalid value for `max_maj` argument: {0}'.format(max_maj))
if positions is None:
positions = list(map(float, range(align.ls)))
elif len(positions) != (struct.get_ni() + struct.get_no()):
raise ValueError('list of positions does not have the right number of items')
if stats in ['D', 'Dp', 'r', 'rsq']:
multi = False
stats = [stats]
else:
multi = True
# make a list of variable sites
genosite = _eggwrapper.Genotypes()
genosites = [] # need to be kept to perform calculations
site = _site.Site()
final_positions = []
sd = _eggwrapper.SiteDiversity()
frq = _eggwrapper.FreqHolder()
frq.setup_structure(struct)
for i in range(align.ls):
site.from_align(align, i)
genosite.process(site._obj, struct)
frq.process_site(genosite.site())
if (sd.process(frq)&2) != 0 and sd.Aing() > 1.0:
final_positions.append(positions[i])
mLD.load(genosite, positions[i])
genosites.append(genosite)
genosite = _eggwrapper.Genotypes()
matrix = [[None for j in range(i+1)] for i in range(len(genosites))]
# compute LD
mLD.computeLD(min_n, max_maj)
# extract requested values
for i in range(mLD.num_pairs()):
pld = mLD.pairLD(i)
idx2 = mLD.index1(i)
idx1 = mLD.index2(i) # reverse indexes
computed_stats = _get_stats(pld, multiple_policy, min_freq)
matrix[idx1][idx2] = []
for stat in stats:
if stat == 'd': matrix[idx1][idx2].append( final_positions[idx1] - final_positions[idx2] )
elif stat == 'D': matrix[idx1][idx2].append( computed_stats['D'] )
elif stat == 'Dp': matrix[idx1][idx2].append( computed_stats['Dp'] )
elif stat == 'r': matrix[idx1][idx2].append( computed_stats['r'] )
elif stat == 'rsq': matrix[idx1][idx2].append( computed_stats['rsq'] )
else: raise ValueError('invalid statistic code: `{0}`'.format(stat))
if not multi:
matrix[idx1][idx2] = matrix[idx1][idx2][0]
# return
return final_positions, matrix
```