def test_sequence_divergence(self):
from allel.stats import sequence_divergence
pos = [2, 4, 8]
ac1 = AlleleCountsArray([[2, 0],
[2, 0],
[2, 0]])
ac2 = AlleleCountsArray([[0, 2],
[0, 2],
[0, 2]])
# all variants
e = 3 / 7
a = sequence_divergence(pos, ac1, ac2)
eq(e, a)
# start/stop
e = 2 / 6
a = sequence_divergence(pos, ac1, ac2, start=0, stop=5)
eq(e, a)
# start/stop, an provided
an1 = ac1.sum(axis=1)
an2 = ac2.sum(axis=1)
e = 2 / 6
a = sequence_divergence(pos, ac1, ac2, start=0, stop=5, an1=an1,
an2=an2)
eq(e, a)
def patterson_f2(aca, acb):
"""Unbiased estimator for F2(A, B), the branch length between populations
A and B.
Parameters
----------
aca : array_like, int, shape (n_variants, 2)
Allele counts for population A.
acb : array_like, int, shape (n_variants, 2)
Allele counts for population B.
Returns
-------
f2 : ndarray, float, shape (n_variants,)
Notes
-----
See Patterson (2012), Appendix A.
"""
# check inputs
aca = AlleleCountsArray(aca, copy=False)
assert aca.shape[1] == 2, 'only biallelic variants supported'
acb = AlleleCountsArray(acb, copy=False)
assert acb.shape[1] == 2, 'only biallelic variants supported'
check_dim0_aligned(aca, acb)
# compute allele numbers
sa = aca.sum(axis=1)
sb = acb.sum(axis=1)
# compute heterozygosities
ha = h_hat(aca)
hb = h_hat(acb)
# compute sample frequencies for the alternate allele
a = aca.to_frequencies()[:, 1]
b = acb.to_frequencies()[:, 1]
# compute estimator
x = ((a - b)**2) - (ha / sa) - (hb / sb)
return x
def patterson_f2(aca, acb):
"""Unbiased estimator for F2(A, B), the branch length between populations
A and B.
Parameters
----------
aca : array_like, int, shape (n_variants, 2)
Allele counts for population A.
acb : array_like, int, shape (n_variants, 2)
Allele counts for population B.
Returns
-------
f2 : ndarray, float, shape (n_variants,)
Notes
-----
See Patterson (2012), Appendix A.
"""
# check inputs
aca = AlleleCountsArray(aca, copy=False)
assert aca.shape[1] == 2, 'only biallelic variants supported'
acb = AlleleCountsArray(acb, copy=False)
assert acb.shape[1] == 2, 'only biallelic variants supported'
check_dim0_aligned(aca, acb)
# compute allele numbers
sa = aca.sum(axis=1)
sb = acb.sum(axis=1)
# compute heterozygosities
ha = h_hat(aca)
hb = h_hat(acb)
# compute sample frequencies for the alternate allele
a = aca.to_frequencies()[:, 1]
b = acb.to_frequencies()[:, 1]
# compute estimator
x = ((a - b) ** 2) - (ha / sa) - (hb / sb)
return x
def patterson_f3(acc, aca, acb):
"""Unbiased estimator for F3(C; A, B), the three-population test for
admixture in population C.
Parameters
----------
acc : array_like, int, shape (n_variants, 2)
Allele counts for the test population (C).
aca : array_like, int, shape (n_variants, 2)
Allele counts for the first source population (A).
acb : array_like, int, shape (n_variants, 2)
Allele counts for the second source population (B).
Returns
-------
T : ndarray, float, shape (n_variants,)
Un-normalized f3 estimates per variant.
B : ndarray, float, shape (n_variants,)
Estimates for heterozygosity in population C.
Notes
-----
See Patterson (2012), main text and Appendix A.
For un-normalized f3 statistics, ignore the `B` return value.
To compute the f3* statistic, which is normalized by heterozygosity in
population C to remove numerical dependence on the allele frequency
spectrum, compute ``np.sum(T) / np.sum(B)``.
"""
# check inputs
aca = AlleleCountsArray(aca, copy=False)
assert aca.shape[1] == 2, 'only biallelic variants supported'
acb = AlleleCountsArray(acb, copy=False)
assert acb.shape[1] == 2, 'only biallelic variants supported'
acc = AlleleCountsArray(acc, copy=False)
assert acc.shape[1] == 2, 'only biallelic variants supported'
check_dim0_aligned(aca, acb, acc)
# compute allele number and heterozygosity in test population
sc = acc.sum(axis=1)
hc = h_hat(acc)
# compute sample frequencies for the alternate allele
a = aca.to_frequencies()[:, 1]
b = acb.to_frequencies()[:, 1]
c = acc.to_frequencies()[:, 1]
# compute estimator
T = ((c - a) * (c - b)) - (hc / sc)
B = 2 * hc
return T, B
def patterson_f3(acc, aca, acb):
"""Unbiased estimator for F3(C; A, B), the three-population test for
admixture in population C.
Parameters
----------
acc : array_like, int, shape (n_variants, 2)
Allele counts for the test population (C).
aca : array_like, int, shape (n_variants, 2)
Allele counts for the first source population (A).
acb : array_like, int, shape (n_variants, 2)
Allele counts for the second source population (B).
Returns
-------
T : ndarray, float, shape (n_variants,)
Un-normalized f3 estimates per variant.
B : ndarray, float, shape (n_variants,)
Estimates for heterozygosity in population C.
Notes
-----
See Patterson (2012), main text and Appendix A.
For un-normalized f3 statistics, ignore the `B` return value.
To compute the f3* statistic, which is normalized by heterozygosity in
population C to remove numerical dependence on the allele frequency
spectrum, compute ``np.sum(T) / np.sum(B)``.
"""
# check inputs
aca = AlleleCountsArray(aca, copy=False)
assert aca.shape[1] == 2, 'only biallelic variants supported'
acb = AlleleCountsArray(acb, copy=False)
assert acb.shape[1] == 2, 'only biallelic variants supported'
acc = AlleleCountsArray(acc, copy=False)
assert acc.shape[1] == 2, 'only biallelic variants supported'
check_dim0_aligned(aca, acb, acc)
# compute allele number and heterozygosity in test population
sc = acc.sum(axis=1)
hc = h_hat(acc)
# compute sample frequencies for the alternate allele
a = aca.to_frequencies()[:, 1]
b = acb.to_frequencies()[:, 1]
c = acc.to_frequencies()[:, 1]
# compute estimator
T = ((c - a) * (c - b)) - (hc / sc)
B = 2 * hc
return T, B
def windowed_tajima_d(pos, ac, size=None, start=None, stop=None, step=None, windows=None, fill=np.nan):
"""Calculate the value of Tajima's D in windows over a single
chromosome/contig.
Parameters
----------
pos : array_like, int, shape (n_items,)
Variant positions, using 1-based coordinates, in ascending order.
ac : array_like, int, shape (n_variants, n_alleles)
Allele counts array.
size : int, optional
The window size (number of bases).
start : int, optional
The position at which to start (1-based).
stop : int, optional
The position at which to stop (1-based).
step : int, optional
The distance between start positions of windows. If not given,
defaults to the window size, i.e., non-overlapping windows.
windows : array_like, int, shape (n_windows, 2), optional
Manually specify the windows to use as a sequence of (window_start,
window_stop) positions, using 1-based coordinates. Overrides the
size/start/stop/step parameters.
fill : object, optional
The value to use where a window is completely inaccessible.
Returns
-------
D : ndarray, float, shape (n_windows,)
Tajima's D.
windows : ndarray, int, shape (n_windows, 2)
The windows used, as an array of (window_start, window_stop) positions,
using 1-based coordinates.
counts : ndarray, int, shape (n_windows,)
Number of variants in each window.
Examples
--------
>>> import allel
>>> g = allel.GenotypeArray([[[0, 0], [0, 0]],
... [[0, 0], [0, 1]],
... [[0, 0], [1, 1]],
... [[0, 1], [1, 1]],
... [[1, 1], [1, 1]],
... [[0, 0], [1, 2]],
... [[0, 1], [1, 2]],
... [[0, 1], [-1, -1]],
... [[-1, -1], [-1, -1]]])
>>> ac = g.count_alleles()
>>> pos = [2, 4, 7, 14, 15, 18, 19, 25, 27]
>>> D, windows, counts = allel.stats.windowed_tajima_d(
... pos, ac, size=10, start=1, stop=31
... )
>>> D
array([ 0.59158014, 2.93397641, 6.12372436])
>>> windows
array([[ 1, 10],
[11, 20],
[21, 31]])
>>> counts
array([3, 4, 2])
"""
# check inputs
if not isinstance(pos, SortedIndex):
pos = SortedIndex(pos, copy=False)
if not hasattr(ac, "count_segregating"):
ac = AlleleCountsArray(ac, copy=False)
# assume number of chromosomes sampled is constant for all variants
n = ac.sum(axis=1).max()
# calculate constants
a1 = np.sum(1 / np.arange(1, n))
a2 = np.sum(1 / (np.arange(1, n) ** 2))
b1 = (n + 1) / (3 * (n - 1))
b2 = 2 * (n ** 2 + n + 3) / (9 * n * (n - 1))
c1 = b1 - (1 / a1)
c2 = b2 - ((n + 2) / (a1 * n)) + (a2 / (a1 ** 2))
e1 = c1 / a1
e2 = c2 / (a1 ** 2 + a2)
# locate segregating variants
is_seg = ac.is_segregating()
# calculate mean pairwise difference
mpd = mean_pairwise_difference(ac, fill=0)
# define statistic to compute for each window
# noinspection PyPep8Naming
def statistic(w_is_seg, w_mpd):
S = np.count_nonzero(w_is_seg)
pi = np.sum(w_mpd)
d = pi - (S / a1)
d_stdev = np.sqrt((e1 * S) + (e2 * S * (S - 1)))
wD = d / d_stdev
return wD
D, windows, counts = windowed_statistic(
pos,
values=(is_seg, mpd),
statistic=statistic,
size=size,
start=start,
stop=stop,
step=step,
windows=windows,
fill=fill,
)
return D, windows, counts
def tajima_d(ac, pos=None, start=None, stop=None):
"""Calculate the value of Tajima's D over a given region.
Parameters
----------
ac : array_like, int, shape (n_variants, n_alleles)
Allele counts array.
pos : array_like, int, shape (n_items,), optional
Variant positions, using 1-based coordinates, in ascending order.
start : int, optional
The position at which to start (1-based).
stop : int, optional
The position at which to stop (1-based).
Returns
-------
D : float
Examples
--------
>>> import allel
>>> g = allel.GenotypeArray([[[0, 0], [0, 0]],
... [[0, 0], [0, 1]],
... [[0, 0], [1, 1]],
... [[0, 1], [1, 1]],
... [[1, 1], [1, 1]],
... [[0, 0], [1, 2]],
... [[0, 1], [1, 2]],
... [[0, 1], [-1, -1]],
... [[-1, -1], [-1, -1]]])
>>> ac = g.count_alleles()
>>> allel.stats.tajima_d(ac)
3.1445848780213814
>>> pos = [2, 4, 7, 14, 15, 18, 19, 25, 27]
>>> allel.stats.tajima_d(ac, pos=pos, start=7, stop=25)
3.8779735196179366
"""
# check inputs
if not hasattr(ac, "count_segregating"):
ac = AlleleCountsArray(ac, copy=False)
# deal with subregion
if pos is not None and (start is not None or stop is not None):
if not isinstance(pos, SortedIndex):
pos = SortedIndex(pos, copy=False)
loc = pos.locate_range(start, stop)
ac = ac[loc]
# assume number of chromosomes sampled is constant for all variants
n = ac.sum(axis=1).max()
# count segregating variants
S = ac.count_segregating()
# (n-1)th harmonic number
a1 = np.sum(1 / np.arange(1, n))
# calculate Watterson's theta (absolute value)
theta_hat_w_abs = S / a1
# calculate mean pairwise difference
mpd = mean_pairwise_difference(ac, fill=0)
# calculate theta_hat pi (sum differences over variants)
theta_hat_pi_abs = np.sum(mpd)
# N.B., both theta estimates are usually divided by the number of
# (accessible) bases but here we want the absolute difference
d = theta_hat_pi_abs - theta_hat_w_abs
# calculate the denominator (standard deviation)
a2 = np.sum(1 / (np.arange(1, n) ** 2))
b1 = (n + 1) / (3 * (n - 1))
b2 = 2 * (n ** 2 + n + 3) / (9 * n * (n - 1))
c1 = b1 - (1 / a1)
c2 = b2 - ((n + 2) / (a1 * n)) + (a2 / (a1 ** 2))
e1 = c1 / a1
e2 = c2 / (a1 ** 2 + a2)
d_stdev = np.sqrt((e1 * S) + (e2 * S * (S - 1)))
# finally calculate Tajima's D
D = d / d_stdev
return D
def windowed_watterson_theta(
pos, ac, size=None, start=None, stop=None, step=None, windows=None, is_accessible=None, fill=np.nan
):
"""Calculate the value of Watterson's estimator in windows over a single
chromosome/contig.
Parameters
----------
pos : array_like, int, shape (n_items,)
Variant positions, using 1-based coordinates, in ascending order.
ac : array_like, int, shape (n_variants, n_alleles)
Allele counts array.
size : int, optional
The window size (number of bases).
start : int, optional
The position at which to start (1-based).
stop : int, optional
The position at which to stop (1-based).
step : int, optional
The distance between start positions of windows. If not given,
defaults to the window size, i.e., non-overlapping windows.
windows : array_like, int, shape (n_windows, 2), optional
Manually specify the windows to use as a sequence of (window_start,
window_stop) positions, using 1-based coordinates. Overrides the
size/start/stop/step parameters.
is_accessible : array_like, bool, shape (len(contig),), optional
Boolean array indicating accessibility status for all positions in the
chromosome/contig.
fill : object, optional
The value to use where a window is completely inaccessible.
Returns
-------
theta_hat_w : ndarray, float, shape (n_windows,)
Watterson's estimator (theta hat per base).
windows : ndarray, int, shape (n_windows, 2)
The windows used, as an array of (window_start, window_stop) positions,
using 1-based coordinates.
n_bases : ndarray, int, shape (n_windows,)
Number of (accessible) bases in each window.
counts : ndarray, int, shape (n_windows,)
Number of variants in each window.
Examples
--------
>>> import allel
>>> g = allel.GenotypeArray([[[0, 0], [0, 0]],
... [[0, 0], [0, 1]],
... [[0, 0], [1, 1]],
... [[0, 1], [1, 1]],
... [[1, 1], [1, 1]],
... [[0, 0], [1, 2]],
... [[0, 1], [1, 2]],
... [[0, 1], [-1, -1]],
... [[-1, -1], [-1, -1]]])
>>> ac = g.count_alleles()
>>> pos = [2, 4, 7, 14, 15, 18, 19, 25, 27]
>>> theta_hat_w, windows, n_bases, counts = allel.stats.windowed_watterson_theta(
... pos, ac, size=10, start=1, stop=31
... )
>>> theta_hat_w
array([ 0.10909091, 0.16363636, 0.04958678])
>>> windows
array([[ 1, 10],
[11, 20],
[21, 31]])
>>> n_bases
array([10, 10, 11])
>>> counts
array([3, 4, 2])
""" # flake8: noqa
# check inputs
if not isinstance(pos, SortedIndex):
pos = SortedIndex(pos, copy=False)
is_accessible = asarray_ndim(is_accessible, 1, allow_none=True)
if not hasattr(ac, "count_segregating"):
ac = AlleleCountsArray(ac, copy=False)
# locate segregating variants
is_seg = ac.is_segregating()
# count segregating variants in windows
S, windows, counts = windowed_statistic(
pos, is_seg, statistic=np.count_nonzero, size=size, start=start, stop=stop, step=step, windows=windows, fill=0
)
# assume number of chromosomes sampled is constant for all variants
n = ac.sum(axis=1).max()
# (n-1)th harmonic number
a1 = np.sum(1 / np.arange(1, n))
# absolute value of Watterson's theta
theta_hat_w_abs = S / a1
# theta per base
theta_hat_w, n_bases = per_base(theta_hat_w_abs, windows=windows, is_accessible=is_accessible, fill=fill)
return theta_hat_w, windows, n_bases, counts
def watterson_theta(pos, ac, start=None, stop=None, is_accessible=None):
"""Calculate the value of Watterson's estimator over a given region.
Parameters
----------
pos : array_like, int, shape (n_items,)
Variant positions, using 1-based coordinates, in ascending order.
ac : array_like, int, shape (n_variants, n_alleles)
Allele counts array.
start : int, optional
The position at which to start (1-based).
stop : int, optional
The position at which to stop (1-based).
is_accessible : array_like, bool, shape (len(contig),), optional
Boolean array indicating accessibility status for all positions in the
chromosome/contig.
Returns
-------
theta_hat_w : float
Watterson's estimator (theta hat per base).
Examples
--------
>>> import allel
>>> g = allel.GenotypeArray([[[0, 0], [0, 0]],
... [[0, 0], [0, 1]],
... [[0, 0], [1, 1]],
... [[0, 1], [1, 1]],
... [[1, 1], [1, 1]],
... [[0, 0], [1, 2]],
... [[0, 1], [1, 2]],
... [[0, 1], [-1, -1]],
... [[-1, -1], [-1, -1]]])
>>> ac = g.count_alleles()
>>> pos = [2, 4, 7, 14, 15, 18, 19, 25, 27]
>>> theta_hat_w = allel.stats.watterson_theta(pos, ac, start=1, stop=31)
>>> theta_hat_w
0.10557184750733138
"""
# check inputs
if not isinstance(pos, SortedIndex):
pos = SortedIndex(pos, copy=False)
is_accessible = asarray_ndim(is_accessible, 1, allow_none=True)
if not hasattr(ac, "count_segregating"):
ac = AlleleCountsArray(ac, copy=False)
# deal with subregion
if start is not None or stop is not None:
loc = pos.locate_range(start, stop)
pos = pos[loc]
ac = ac[loc]
if start is None:
start = pos[0]
if stop is None:
stop = pos[-1]
# count segregating variants
S = ac.count_segregating()
# assume number of chromosomes sampled is constant for all variants
n = ac.sum(axis=1).max()
# (n-1)th harmonic number
a1 = np.sum(1 / np.arange(1, n))
# calculate absolute value
theta_hat_w_abs = S / a1
# calculate value per base
if is_accessible is None:
n_bases = stop - start + 1
else:
n_bases = np.count_nonzero(is_accessible[start - 1 : stop])
theta_hat_w = theta_hat_w_abs / n_bases
return theta_hat_w
def tajima_d(ac, pos=None, start=None, stop=None, min_sites=3):
"""Calculate the value of Tajima's D over a given region.
Parameters
----------
ac : array_like, int, shape (n_variants, n_alleles)
Allele counts array.
pos : array_like, int, shape (n_items,), optional
Variant positions, using 1-based coordinates, in ascending order.
start : int, optional
The position at which to start (1-based). Defaults to the first position.
stop : int, optional
The position at which to stop (1-based). Defaults to the last position.
min_sites : int, optional
Minimum number of segregating sites for which to calculate a value. If
there are fewer, np.nan is returned. Defaults to 3.
Returns
-------
D : float
Examples
--------
>>> import allel
>>> g = allel.GenotypeArray([[[0, 0], [0, 0]],
... [[0, 0], [0, 1]],
... [[0, 0], [1, 1]],
... [[0, 1], [1, 1]],
... [[1, 1], [1, 1]],
... [[0, 0], [1, 2]],
... [[0, 1], [1, 2]],
... [[0, 1], [-1, -1]],
... [[-1, -1], [-1, -1]]])
>>> ac = g.count_alleles()
>>> allel.tajima_d(ac)
3.1445848780213814
>>> pos = [2, 4, 7, 14, 15, 18, 19, 25, 27]
>>> allel.tajima_d(ac, pos=pos, start=7, stop=25)
3.8779735196179366
"""
# check inputs
if not hasattr(ac, 'count_segregating'):
ac = AlleleCountsArray(ac, copy=False)
# deal with subregion
if pos is not None and (start is not None or stop is not None):
if not isinstance(pos, SortedIndex):
pos = SortedIndex(pos, copy=False)
loc = pos.locate_range(start, stop)
ac = ac[loc]
# count segregating variants
S = ac.count_segregating()
if S < min_sites:
return np.nan
# assume number of chromosomes sampled is constant for all variants
n = ac.sum(axis=1).max()
# (n-1)th harmonic number
a1 = np.sum(1 / np.arange(1, n))
# calculate Watterson's theta (absolute value)
theta_hat_w_abs = S / a1
# calculate mean pairwise difference
mpd = mean_pairwise_difference(ac, fill=0)
# calculate theta_hat pi (sum differences over variants)
theta_hat_pi_abs = np.sum(mpd)
# N.B., both theta estimates are usually divided by the number of
# (accessible) bases but here we want the absolute difference
d = theta_hat_pi_abs - theta_hat_w_abs
# calculate the denominator (standard deviation)
a2 = np.sum(1 / (np.arange(1, n)**2))
b1 = (n + 1) / (3 * (n - 1))
b2 = 2 * (n**2 + n + 3) / (9 * n * (n - 1))
c1 = b1 - (1 / a1)
c2 = b2 - ((n + 2) / (a1 * n)) + (a2 / (a1**2))
e1 = c1 / a1
e2 = c2 / (a1**2 + a2)
d_stdev = np.sqrt((e1 * S) + (e2 * S * (S - 1)))
# finally calculate Tajima's D
D = d / d_stdev
return D
def windowed_watterson_theta(pos,
ac,
size=None,
start=None,
stop=None,
step=None,
windows=None,
is_accessible=None,
fill=np.nan):
"""Calculate the value of Watterson's estimator in windows over a single
chromosome/contig.
Parameters
----------
pos : array_like, int, shape (n_items,)
Variant positions, using 1-based coordinates, in ascending order.
ac : array_like, int, shape (n_variants, n_alleles)
Allele counts array.
size : int, optional
The window size (number of bases).
start : int, optional
The position at which to start (1-based).
stop : int, optional
The position at which to stop (1-based).
step : int, optional
The distance between start positions of windows. If not given,
defaults to the window size, i.e., non-overlapping windows.
windows : array_like, int, shape (n_windows, 2), optional
Manually specify the windows to use as a sequence of (window_start,
window_stop) positions, using 1-based coordinates. Overrides the
size/start/stop/step parameters.
is_accessible : array_like, bool, shape (len(contig),), optional
Boolean array indicating accessibility status for all positions in the
chromosome/contig.
fill : object, optional
The value to use where a window is completely inaccessible.
Returns
-------
theta_hat_w : ndarray, float, shape (n_windows,)
Watterson's estimator (theta hat per base).
windows : ndarray, int, shape (n_windows, 2)
The windows used, as an array of (window_start, window_stop) positions,
using 1-based coordinates.
n_bases : ndarray, int, shape (n_windows,)
Number of (accessible) bases in each window.
counts : ndarray, int, shape (n_windows,)
Number of variants in each window.
Examples
--------
>>> import allel
>>> g = allel.GenotypeArray([[[0, 0], [0, 0]],
... [[0, 0], [0, 1]],
... [[0, 0], [1, 1]],
... [[0, 1], [1, 1]],
... [[1, 1], [1, 1]],
... [[0, 0], [1, 2]],
... [[0, 1], [1, 2]],
... [[0, 1], [-1, -1]],
... [[-1, -1], [-1, -1]]])
>>> ac = g.count_alleles()
>>> pos = [2, 4, 7, 14, 15, 18, 19, 25, 27]
>>> theta_hat_w, windows, n_bases, counts = allel.windowed_watterson_theta(
... pos, ac, size=10, start=1, stop=31
... )
>>> theta_hat_w
array([0.10909091, 0.16363636, 0.04958678])
>>> windows
array([[ 1, 10],
[11, 20],
[21, 31]])
>>> n_bases
array([10, 10, 11])
>>> counts
array([3, 4, 2])
""" # flake8: noqa
# check inputs
if not isinstance(pos, SortedIndex):
pos = SortedIndex(pos, copy=False)
is_accessible = asarray_ndim(is_accessible, 1, allow_none=True)
if not hasattr(ac, 'count_segregating'):
ac = AlleleCountsArray(ac, copy=False)
# locate segregating variants
is_seg = ac.is_segregating()
# count segregating variants in windows
S, windows, counts = windowed_statistic(pos,
is_seg,
statistic=np.count_nonzero,
size=size,
start=start,
stop=stop,
step=step,
windows=windows,
fill=0)
# assume number of chromosomes sampled is constant for all variants
n = ac.sum(axis=1).max()
# (n-1)th harmonic number
a1 = np.sum(1 / np.arange(1, n))
# absolute value of Watterson's theta
theta_hat_w_abs = S / a1
# theta per base
theta_hat_w, n_bases = per_base(theta_hat_w_abs,
windows=windows,
is_accessible=is_accessible,
fill=fill)
return theta_hat_w, windows, n_bases, counts
def watterson_theta(pos, ac, start=None, stop=None, is_accessible=None):
"""Calculate the value of Watterson's estimator over a given region.
Parameters
----------
pos : array_like, int, shape (n_items,)
Variant positions, using 1-based coordinates, in ascending order.
ac : array_like, int, shape (n_variants, n_alleles)
Allele counts array.
start : int, optional
The position at which to start (1-based). Defaults to the first position.
stop : int, optional
The position at which to stop (1-based). Defaults to the last position.
is_accessible : array_like, bool, shape (len(contig),), optional
Boolean array indicating accessibility status for all positions in the
chromosome/contig.
Returns
-------
theta_hat_w : float
Watterson's estimator (theta hat per base).
Examples
--------
>>> import allel
>>> g = allel.GenotypeArray([[[0, 0], [0, 0]],
... [[0, 0], [0, 1]],
... [[0, 0], [1, 1]],
... [[0, 1], [1, 1]],
... [[1, 1], [1, 1]],
... [[0, 0], [1, 2]],
... [[0, 1], [1, 2]],
... [[0, 1], [-1, -1]],
... [[-1, -1], [-1, -1]]])
>>> ac = g.count_alleles()
>>> pos = [2, 4, 7, 14, 15, 18, 19, 25, 27]
>>> theta_hat_w = allel.watterson_theta(pos, ac, start=1, stop=31)
>>> theta_hat_w
0.10557184750733138
"""
# check inputs
if not isinstance(pos, SortedIndex):
pos = SortedIndex(pos, copy=False)
is_accessible = asarray_ndim(is_accessible, 1, allow_none=True)
if not hasattr(ac, 'count_segregating'):
ac = AlleleCountsArray(ac, copy=False)
# deal with subregion
if start is not None or stop is not None:
loc = pos.locate_range(start, stop)
pos = pos[loc]
ac = ac[loc]
if start is None:
start = pos[0]
if stop is None:
stop = pos[-1]
# count segregating variants
S = ac.count_segregating()
# assume number of chromosomes sampled is constant for all variants
n = ac.sum(axis=1).max()
# (n-1)th harmonic number
a1 = np.sum(1 / np.arange(1, n))
# calculate absolute value
theta_hat_w_abs = S / a1
# calculate value per base
if is_accessible is None:
n_bases = stop - start + 1
else:
n_bases = np.count_nonzero(is_accessible[start - 1:stop])
theta_hat_w = theta_hat_w_abs / n_bases
return theta_hat_w
def windowed_tajima_d(pos,
ac,
size=None,
start=None,
stop=None,
step=None,
windows=None,
min_sites=3):
"""Calculate the value of Tajima's D in windows over a single
chromosome/contig.
Parameters
----------
pos : array_like, int, shape (n_items,)
Variant positions, using 1-based coordinates, in ascending order.
ac : array_like, int, shape (n_variants, n_alleles)
Allele counts array.
size : int, optional
The window size (number of bases).
start : int, optional
The position at which to start (1-based).
stop : int, optional
The position at which to stop (1-based).
step : int, optional
The distance between start positions of windows. If not given,
defaults to the window size, i.e., non-overlapping windows.
windows : array_like, int, shape (n_windows, 2), optional
Manually specify the windows to use as a sequence of (window_start,
window_stop) positions, using 1-based coordinates. Overrides the
size/start/stop/step parameters.
min_sites : int, optional
Minimum number of segregating sites for which to calculate a value. If
there are fewer, np.nan is returned. Defaults to 3.
Returns
-------
D : ndarray, float, shape (n_windows,)
Tajima's D.
windows : ndarray, int, shape (n_windows, 2)
The windows used, as an array of (window_start, window_stop) positions,
using 1-based coordinates.
counts : ndarray, int, shape (n_windows,)
Number of variants in each window.
Examples
--------
>>> import allel
>>> g = allel.GenotypeArray([[[0, 0], [0, 0]],
... [[0, 0], [0, 1]],
... [[0, 0], [1, 1]],
... [[0, 1], [1, 1]],
... [[1, 1], [1, 1]],
... [[0, 0], [1, 2]],
... [[0, 1], [1, 2]],
... [[0, 1], [-1, -1]],
... [[-1, -1], [-1, -1]]])
>>> ac = g.count_alleles()
>>> pos = [2, 4, 7, 14, 15, 20, 22, 25, 27]
>>> D, windows, counts = allel.windowed_tajima_d(pos, ac, size=20, step=10, start=1, stop=31)
>>> D
array([1.36521524, 4.22566622])
>>> windows
array([[ 1, 20],
[11, 31]])
>>> counts
array([6, 6])
"""
# check inputs
if not isinstance(pos, SortedIndex):
pos = SortedIndex(pos, copy=False)
if not hasattr(ac, 'count_segregating'):
ac = AlleleCountsArray(ac, copy=False)
# assume number of chromosomes sampled is constant for all variants
n = ac.sum(axis=1).max()
# calculate constants
a1 = np.sum(1 / np.arange(1, n))
a2 = np.sum(1 / (np.arange(1, n)**2))
b1 = (n + 1) / (3 * (n - 1))
b2 = 2 * (n**2 + n + 3) / (9 * n * (n - 1))
c1 = b1 - (1 / a1)
c2 = b2 - ((n + 2) / (a1 * n)) + (a2 / (a1**2))
e1 = c1 / a1
e2 = c2 / (a1**2 + a2)
# locate segregating variants
is_seg = ac.is_segregating()
# calculate mean pairwise difference
mpd = mean_pairwise_difference(ac, fill=0)
# define statistic to compute for each window
# noinspection PyPep8Naming
def statistic(w_is_seg, w_mpd):
S = np.count_nonzero(w_is_seg)
if S < min_sites:
return np.nan
pi = np.sum(w_mpd)
d = pi - (S / a1)
d_stdev = np.sqrt((e1 * S) + (e2 * S * (S - 1)))
wD = d / d_stdev
return wD
D, windows, counts = windowed_statistic(pos,
values=(is_seg, mpd),
statistic=statistic,
size=size,
start=start,
stop=stop,
step=step,
windows=windows,
fill=np.nan)
return D, windows, counts
