def rgibbs_beta(concentrations, gamma_bar, tausq, n_peptides,
prior_mean=np.array([0., 1.]), prior_prec=np.array([0., 0.]),
prior_trunc_b1=(-np.Inf, np.Inf)):
'''
Gibbs update for slope and intercept of concentration/intensity model.
Relatively standard conjugate Normal regression update, univariate case.
Slight subtlety with the prior on beta_1; having support near 0 is
problematic for the measurement error draw.
'''
# Setup quantities for WLS estimation. Using pseudo-observations for prior.
w = np.r_[n_peptides / tausq, prior_prec]
X = np.ones((np.size(concentrations) + 2, 2))
X[:-2, 1] = concentrations
X[-2, 1] = 0
X[-1, 0] = 0
y = np.r_[gamma_bar, prior_mean]
# Run WLS
estimate = glm.wls(X=X, y=y, w=w)
# Get posterior covariance
Sigma = linalg.cho_solve((estimate['L'], True), np.eye(2))
# Draw beta_1 from truncated distribution
beta = np.empty(2)
beta[1] = np.random.randn(1) * np.sqrt(Sigma[1,1]) + estimate['b'][1]
while beta[1] < prior_trunc_b1[0] or beta[1] > prior_trunc_b1[1]:
beta[1] = np.random.randn(1) * np.sqrt(Sigma[1,1]) + estimate['b'][1]
# Draw beta_0 from conditional posterior given beta_1
beta[0] = np.random.randn(1) * \
np.sqrt(Sigma[0,0] - Sigma[0,1]**2 / Sigma[1,1]) + \
estimate['b'][0] + Sigma[0,1] / Sigma[1,1] * \
(beta[1] - estimate['b'][1])
return beta
def mcmc_serial(intensities_obs, mapping_states_obs, mapping_peptides, cfg,
known_concentrations=None, mapping_known_concentrations=None,
peptide_features=None, **kwargs):
'''
Serial MCMC sampler for posterior of state-level censoring model.
Parameters
----------
- intensities_obs : array_like
A 1d array of length n_obs_states for which each entry contains the
observed (summed) log state intensity.
This must be aligned to mapping_states_obs and all entires must be
> -inf; no missing peptides.
- mapping_states_obs : array_like, 1 dimension, nonnegative ints
A 1d integer array of length n_obs_states for which each entry
contains the index of the peptide that corresponds to the given
observed state. Peptide indices can range over 0 <= i < n_peptides.
Not every peptide index is required to appear in this mapping; only
observed peptides should be included. Also note that peptides are
indexed overall, not within protein.
- mapping_peptides : array_like, 1 dimension, nonnegative ints
A 1d integer array of length n_peptides for which each entry
contains the index of the protein that corresponds to the given
peptide. Protein indices can range over 0 <= i < n_proteins.
Every peptide and protein to be included in the model should be
included here. That is, both observed and unobserved peptides should
appear in this mapping.
- cfg : dictionary
A dictionary (typically generated from a YAML file) containing
priors and settings for the MCMC algorithm. Its exact form will be
documented elsewhere. It will have at least three sections: priors,
containing one entry per parameter, settings, containing settings
for the MCMC algorithm, and init, containing initial values for
certain parameters.
Returns
-------
- draws : dictionary
1- and 2-dimensional ndarrays containing the posterior samples for
each parameter.
- accept_stats : dictionary
Dictionary containing number of acceptances for each MH step.
'''
# Determine whether algorithm is running with supervision
try:
supervised = cfg['priors']['supervised']
except:
print >> sys.stderr, 'Defaulting to unsupervised algorithm'
supervised = False
# If supervised, determine whether to model distribution of concentrations
# If this is False, prior on $\beta_1$ is scaled by $|\beta_1|^{n_{mis}}$.
if supervised:
try:
concentration_dist = cfg['priors']['concentration_dist']
except:
print >> sys.stderr, 'Defaulting to flat prior on concentrations'
concentration_dist = False
# Determine whether peptide features are present and, if so, their size
if peptide_features is None:
n_peptide_features = 0
else:
n_peptide_features = peptide_features.shape[1]
# Convert inputs to np.ndarrays as needed
if type(intensities_obs) is not np.ndarray:
intensities_obs = np.asanyarray(intensities_obs)
if type(mapping_states_obs) is not np.ndarray:
mapping_states_obs = np.asanyarray(mapping_states_obs, dtype=np.int)
if type(mapping_peptides) is not np.ndarray:
mapping_peptides = np.asanyarray(mapping_peptides, dtype=np.int)
# Extract proposal DFs
try:
prop_df_y_mis = cfg['settings']['prop_df_y_mis']
except:
prop_df_y_mis = 5.0
try:
prop_df_eta = cfg['settings']['prop_df_eta']
except:
prop_df_eta = 10.
# Extract dimensions from input
# Number of iterations from cfg
n_iterations = cfg['settings']['n_iterations']
# Number of peptides and proteins from mapping_peptides
n_peptides = np.size(mapping_peptides)
n_proteins = 1 + np.max(mapping_peptides)
# Check for validity of mapping vectors
if (not issubclass(mapping_states_obs.dtype.type, np.integer) or
np.min(mapping_states_obs) < 0 or
np.max(mapping_states_obs) > n_peptides - 1):
raise ValueError('State to peptide mapping (mapping_states_obs)'
' is not valid')
if (not issubclass(mapping_peptides.dtype.type, np.integer) or
np.min(mapping_peptides) < 0 or
np.max(mapping_peptides) > n_peptides - 1):
raise ValueError('Peptide to protein mapping (mapping_peptides)'
' is not valid')
# Compute tabulations that are invariant across iterations
# Total number of observed states
n_obs_states = np.size(intensities_obs)
# Tabulate peptides per protein
n_peptides_per_protein = np.bincount(mapping_peptides)
peptides_obs = np.unique(mapping_states_obs)
n_obs_peptides_per_protein = np.bincount(mapping_peptides[peptides_obs],
minlength=n_proteins)
# Tabulate number of observed states per peptide
n_obs_states_per_peptide = np.bincount(mapping_states_obs,
minlength=n_peptides)
# Sum observed intensities per peptide
total_intensity_obs_per_peptide = np.bincount(mapping_states_obs,
weights=intensities_obs,
minlength=n_peptides)
# Allocate data structures for draws
# Data structures for supervised algorithm
if supervised:
beta_draws = np.empty((n_iterations, 2))
concentration_draws = np.empty((n_iterations, n_proteins))
mean_concentration_draws = np.zeros((n_iterations))
prec_concentration_draws = np.zeros((n_iterations))
# Peptide- and protein-level means
gamma_draws = np.empty((n_iterations, n_peptides))
mu_draws = np.empty((n_iterations, n_proteins))
# Number of censored states per peptide
n_cen_states_per_peptide_draws = np.zeros((n_iterations, n_peptides),
dtype=np.integer)
# State- and peptide-level variances
sigmasq_draws = np.empty((n_iterations, n_proteins))
tausq_draws = np.empty((n_iterations, n_proteins))
# Hyperparameters for state-level variance model
shape_sigmasq = np.empty(n_iterations)
rate_sigmasq = np.empty(n_iterations)
# Hyperparameters for peptide-level variance model
shape_tausq = np.empty(n_iterations)
rate_tausq = np.empty(n_iterations)
# Censoring probability model parameters
eta_draws = np.zeros((n_iterations, 2 + n_peptide_features * 2))
p_rnd_cen = np.empty(n_iterations)
# Number of states model parameters
r = np.empty(n_iterations)
lmbda = np.empty(n_iterations)
# Compute initial values for MCMC iterations
# p_rnd_cen from cfg
p_rnd_cen[0] = cfg['init']['p_rnd_cen']
# eta from cfg; bivariate normal draw
eta0 = cfg['init']['eta']
eta_draws[0, 0] = eta0['mean'][0] + eta0['sd'][0] * np.random.randn(1)
eta_draws[0, 1] = eta0['mean'][1]
if eta0['sd'][1] > 0:
eta_draws[0, 1] += (eta0['cor'] * eta0['sd'][1] / eta0['sd'][0] *
(eta_draws[0, 0] - eta0['mean'][0]))
eta_draws[0, 1] += (np.sqrt(1. - eta0['cor'] ** 2) * eta0['sd'][1] *
np.random.randn(1))
# Number of states parameters from MAP estimator based on number of observed
# peptides; very crude, but not altogether terrible. Note that this ignores
# the +1 location shift in the actual n_states distribution.
kwargs = {'x': n_obs_states_per_peptide[n_obs_states_per_peptide > 0] - 1,
'transform': True}
kwargs.update(cfg['priors']['n_states_dist'])
r[0], lmbda[0] = lib.map_estimator_nbinom(**kwargs)
lmbda[0] = 1. - lmbda[0]
# Hyperparameters for state- and peptide-level variance distributions
# directly from cfg
shape_sigmasq[0], rate_sigmasq[0] = (
cfg['init']['sigmasq_dist']['shape'],
cfg['init']['sigmasq_dist']['rate'])
shape_tausq[0], rate_tausq[0] = (cfg['init']['tausq_dist']['shape'],
cfg['init']['tausq_dist']['rate'])
# State- and peptide-level variances via inverse-gamma draws
sigmasq_draws[0] = 1. / np.random.gamma(shape=shape_sigmasq[0],
scale=1. / rate_sigmasq[0],
size=n_proteins)
tausq_draws[0] = 1. / np.random.gamma(shape=shape_tausq[0],
scale=1. / rate_tausq[0],
size=n_proteins)
# Mapping from protein to peptide conditional variances for convenience
var_peptide_conditional = sigmasq_draws[0, mapping_peptides]
# Protein-level means using mean observed intensity; excluding missing
# peptides
mu_draws[0] = (np.bincount(mapping_peptides,
total_intensity_obs_per_peptide /
np.maximum(1, n_obs_states_per_peptide)) /
n_obs_peptides_per_protein)
mu_draws[0, n_obs_peptides_per_protein < 1] = np.nanmin(mu_draws[0])
if supervised:
# Simple initialization for supervised algorithm
# Initialize beta from regression of mu against known concentrations
X = np.ones((known_concentrations.size, 2))
X[:,1] = known_concentrations
beta_draws[0] = glm.wls(X=X,
y=mu_draws[0, mapping_known_concentrations],
w=1.)['b']
# Adjust known concentrations in mu accordingly
mu_draws[0, mapping_known_concentrations] = beta_draws[0,0] + \
beta_draws[0,1] * known_concentrations
# And, initialize the concentration draws using the updates mu's
concentration_draws[0] = (mu_draws[0] - beta_draws[0,0]) / \
beta_draws[0,1]
if concentration_dist:
# Initialize hyperparameters on concentration distribution
mean_concentration_draws[0] = np.mean(concentration_draws[0])
prec_concentration_draws[0] = 1. / np.var(concentration_draws[0])
# Peptide-level means using mean observed intensity; imputing missing
# peptides as protein observed means
gamma_draws[0] = mu_draws[0, mapping_peptides]
gamma_draws[0, peptides_obs] = (
total_intensity_obs_per_peptide[peptides_obs] /
n_obs_states_per_peptide[peptides_obs])
# Instantiate GLM family for eta step
try:
glm_link_name = cfg["priors"]["glm_link"].title()
except:
print >> sys.stderr, "GLM link not specified; defaulting to logit"
glm_link_name = "Logit"
glm_link = getattr(glm.links, glm_link_name)
glm_family = glm.families.Binomial(link=glm_link)
# Setup function for prior log density on eta, if requested
try:
prior_scale = cfg["priors"]["eta"]["prior_scale"]
prior_center = cfg["priors"]["eta"]["prior_center"]
except:
prior_scale = None
prior_center = None
if prior_scale is not None:
# Gelman's weakly-informative prior (2008)
def dprior_eta(eta, prior_scale=5., prior_center=0.):
return -np.log(1. + ((eta[1] - prior_center) / prior_scale)**2)
prior_eta_kwargs = {'prior_scale': prior_scale,
'prior_center': prior_center}
else:
dprior_eta = None
prior_eta_kwargs = {}
# Initialize dictionary for acceptance statistics
accept_stats = {'sigmasq_dist': 0,
'tausq_dist': 0,
'n_states_dist': 0,
'eta': 0}
# Master loop for MCMC iterations
for t in xrange(1, n_iterations):
# (1) Draw missing data (n_cen and censored state intensities) given all
# other parameters. Exact draw via rejection samplers.
# (1a) Obtain p_int_cen per peptide and approximatations of censored
# intensity posteriors.
eta_0_effective = eta_draws[t - 1, 0]
eta_1_effective = eta_draws[t - 1, 1]
if n_peptide_features > 0:
eta_0_effective += np.dot(
peptide_features, eta_draws[t - 1, 2:(2 + n_peptide_features)]
)
eta_1_effective += np.dot(
peptide_features, eta_draws[t - 1, (2 + n_peptide_features):]
)
kwargs = {'eta_0': eta_0_effective,
'eta_1': eta_1_effective,
'mu': gamma_draws[t - 1],
'sigmasq': var_peptide_conditional,
'glm_link_name': glm_link_name}
cen_dist = lib.characterize_censored_intensity_dist(**kwargs)
# (1b) Draw number of censored states per peptide
n_cen_states_per_peptide = lib.rncen(n_obs=n_obs_states_per_peptide,
p_rnd_cen=p_rnd_cen[t - 1],
p_int_cen=cen_dist['p_int_cen'],
lmbda=lmbda[t - 1], r=r[t - 1])
n_cen_states_per_peptide_draws[t] = n_cen_states_per_peptide
# Update state-level counts
n_states_per_peptide = (n_obs_states_per_peptide +
n_cen_states_per_peptide)
n_states_per_protein = np.bincount(mapping_peptides,
weights=n_states_per_peptide)
n_states = np.sum(n_states_per_peptide)
# (1c) Draw censored intensities
kwargs['n_cen'] = n_cen_states_per_peptide
kwargs['p_rnd_cen'] = p_rnd_cen[t - 1]
kwargs['propDf'] = prop_df_y_mis
kwargs.update(cen_dist)
intensities_cen, mapping_states_cen, W = lib.rintensities_cen(**kwargs)
# (2) Update random censoring probability. Gibbs step.
p_rnd_cen[t] = updates.rgibbs_p_rnd_cen(n_rnd_cen=np.sum(W),
n_states=n_states,
**cfg['priors']['p_rnd_cen'])
# Sum observed intensities per peptide
total_intensity_cen_per_peptide = np.bincount(mapping_states_cen,
weights=intensities_cen,
minlength=n_peptides)
# Compute mean intensities per peptide
mean_intensity_per_peptide = ((total_intensity_obs_per_peptide +
total_intensity_cen_per_peptide) /
n_states_per_peptide)
# (3) Update peptide-level mean parameters (gamma). Gibbs step.
gamma_draws[t] = updates.rgibbs_gamma(
mu=mu_draws[t - 1, mapping_peptides],
tausq=tausq_draws[t - 1, mapping_peptides],
sigmasq=var_peptide_conditional,
y_bar=mean_intensity_per_peptide,
n_states=n_states_per_peptide)
mean_gamma_by_protein = np.bincount(mapping_peptides,
weights=gamma_draws[t])
mean_gamma_by_protein /= n_peptides_per_protein
# (4) Update protein-level concentrations
if supervised:
if concentration_dist:
# (4a) Update coefficients given concentrations. Gibbs step.
# Only yields sane answers if modeling distribution of
# concentrations.
beta_draws[t] = updates.rgibbs_beta(
concentrations=concentration_draws[t-1],
gamma_bar=mean_gamma_by_protein, tausq=tausq_draws[t - 1],
n_peptides=n_peptides_per_protein,
**cfg['priors']['beta_concentration'])
else:
# (4a) Update coefficients given concentrations. Gibbs step.
# Rao-Blackwellized version, implicitly scaling prior on
# $\beta_1$ by $|\beta_1|^{n_{mis}}
beta_draws[t] = updates.rgibbs_beta(
concentrations=known_concentrations,
gamma_bar=mean_gamma_by_protein[
mapping_known_concentrations],
tausq=tausq_draws[t - 1, mapping_known_concentrations],
n_peptides=n_peptides_per_protein[
mapping_known_concentrations],
**cfg['priors']['beta_concentration'])
# (4b) Update concentrations given coefficients. Gibbs step.
concentration_draws[t] = updates.rgibbs_concentration(
gamma_bar=mean_gamma_by_protein, tausq=tausq_draws[t - 1],
n_peptides=n_peptides_per_protein, beta=beta_draws[t],
mean_concentration=mean_concentration_draws[t-1],
prec_concentration=prec_concentration_draws[t-1])
concentration_draws[t, mapping_known_concentrations] = \
known_concentrations
if concentration_dist:
# (4c) Update concentration distribution hyperparameters
mean_concentration_draws[t] = np.random.normal(
loc=np.mean(concentration_draws[t]),
scale=np.sqrt(1. / prec_concentration_draws[t-1] /
n_proteins), size=1)
prec_concentration_draws[t] = 1. / updates.rgibbs_variances(
rss=np.sum((concentration_draws[t] -
mean_concentration_draws[t])**2),
n=n_proteins,
**cfg['priors']['prec_concentration'])
# Set mu based on concentrations and betas
mu_draws[t] = \
beta_draws[t,0] + beta_draws[t,1] * concentration_draws[t]
else:
# (4) Update protein-level mean parameters (mu). Gibbs step.
mu_draws[t] = updates.rgibbs_mu(gamma_bar=mean_gamma_by_protein,
tausq=tausq_draws[t - 1],
n_peptides=n_peptides_per_protein,
**cfg['priors']['mu'])
# (5) Update state-level variance parameters (sigmasq). Gibbs step.
rss_by_state = (
intensities_obs - gamma_draws[t, mapping_states_obs]) ** 2
rss_by_protein = np.bincount(mapping_peptides[mapping_states_obs],
weights=rss_by_state,
minlength=n_proteins)
rss_by_state = (
intensities_cen - gamma_draws[t, mapping_states_cen]) ** 2
rss_by_protein += np.bincount(mapping_peptides[mapping_states_cen],
weights=rss_by_state,
minlength=n_proteins)
sigmasq_draws[t] = updates.rgibbs_variances(
rss=rss_by_protein, n=n_states_per_protein,
prior_shape=shape_sigmasq[ t - 1], prior_rate=rate_sigmasq[t - 1])
# Mapping from protein to peptide conditional variances for convenience
var_peptide_conditional = sigmasq_draws[t, mapping_peptides]
# (6) Update peptide-level variance parameters (tausq). Gibbs step.
rss_by_peptide = (gamma_draws[t] - mu_draws[t, mapping_peptides]) ** 2
rss_by_protein = np.bincount(mapping_peptides, weights=rss_by_peptide)
tausq_draws[t] = updates.rgibbs_variances(
rss=rss_by_protein, n=n_peptides_per_protein,
prior_shape=shape_tausq[ t - 1], prior_rate=rate_tausq[t - 1])
# (7) Update state-level variance hyperparameters (sigmasq
# distribution). Conditional independence-chain MH step.
result = updates.rmh_variance_hyperparams(
variances=sigmasq_draws[t], shape_prev=shape_sigmasq[ t - 1],
rate_prev=rate_sigmasq[ t - 1], **cfg['priors']['sigmasq_dist'])
(shape_sigmasq[t], rate_sigmasq[t]), accept = result
accept_stats['sigmasq_dist'] += accept
# (8) Update peptide-level variance hyperparameters (tausq
# distribution). Conditional independence-chain MH step.
result = updates.rmh_variance_hyperparams(
variances=tausq_draws[t], shape_prev=shape_tausq[ t - 1],
rate_prev=rate_tausq[t - 1], **cfg['priors']['tausq_dist'])
(shape_tausq[t], rate_tausq[t]), accept = result
accept_stats['tausq_dist'] += accept
# (9) Update parameter for negative-binomial n_states distribution (r
# and lmbda). Conditional independence-chain MH step.
result = updates.rmh_nbinom_hyperparams(
x=n_states_per_peptide - 1,
r_prev=r[ t - 1], p_prev=1. - lmbda[t - 1],
**cfg['priors']['n_states_dist'])
(r[t], lmbda[t]), accept = result
lmbda[t] = 1. - lmbda[t]
accept_stats['n_states_dist'] += accept
# (10) Update coefficients of intensity-based probabilistic censoring
# model (eta). Conditional independence-chain MH step.
# (10a) Build design matrix and response. Only using observed and
# intensity-censored states.
n_at_risk = n_obs_states + np.sum(W < 1)
X = np.zeros((n_at_risk + n_peptide_features * 2,
2 + n_peptide_features * 2))
X[:n_at_risk, 0] = 1.
X[:n_at_risk, 1] = np.r_[intensities_obs, intensities_cen[W < 1]]
if n_peptide_features > 0:
peptide_features_by_state = peptide_features[
np.r_[mapping_states_obs, mapping_states_cen[W < 1]]
]
X[:n_at_risk, 2:(2 + n_peptide_features)] = \
peptide_features_by_state
X[:n_at_risk, (2 + n_peptide_features):] = \
(peptide_features_by_state.T * X[:n_at_risk, 1]).T
X[n_at_risk:, 2:] = np.eye(n_peptide_features * 2)
y = np.zeros(n_at_risk + n_peptide_features * 2)
y[:n_obs_states] = 1.
if n_peptide_features > 0:
y[n_at_risk:] = 0.5
w = np.ones_like(y)
if n_peptide_features > 0:
w[n_at_risk:(n_at_risk + n_peptide_features)] = \
cfg['priors']['eta_features']['primary_pseudoobs']
w[(n_at_risk + n_peptide_features):] = \
cfg['priors']['eta_features']['interaction_pseudoobs']
# (10b) Estimate GLM parameters.
fit_eta = glm.glm(y=y, X=X, w=w, family=glm_family, info=True)
if np.all(np.isfinite(fit_eta['b_hat'])):
# (10c) Execute MH step.
eta_draws[t], accept = glm.mh_update_glm_coef(
b_prev=eta_draws[t - 1], y=y, X=X, family=glm_family,
propDf=prop_df_eta, prior_log_density=dprior_eta,
prior_kwargs=prior_eta_kwargs, **fit_eta)
accept_stats['eta'] += accept
else:
eta_draws[t] = eta_draws[t-1]
if (cfg['settings']['verbose'] > 0 and
t % cfg['settings']['verbose_interval'] == 0):
print >> sys.stderr, 'Iteration %d complete' % t
# Build dictionary of draws to return
draws = {'mu': mu_draws,
'gamma': gamma_draws,
'eta': eta_draws,
'p_rnd_cen': p_rnd_cen,
'lmbda': lmbda,
'r': r,
'sigmasq': sigmasq_draws,
'tausq': tausq_draws,
'n_cen_states_per_peptide': n_cen_states_per_peptide_draws,
'shape_tausq': shape_tausq,
'rate_tausq': rate_tausq,
'shape_sigmasq': shape_sigmasq,
'rate_sigmasq': rate_sigmasq}
# Add additional information for supervised algorithm
if supervised:
draws.update({
'beta': beta_draws,
'concentration': concentration_draws})
if concentration_dist:
draws.update({
'mean_concentration': mean_concentration_draws,
'var_concentration': 1. / prec_concentration_draws})
return (draws, accept_stats)
