def kullback_leibler_divergence(nk, qk, estimator='nsb'):
"""
Kullback-Leibler divergence given counts nk and a reference PMF qk.
Return an estimate of the Kullback-Leibler given an array of counts nk and
a reference PMF qk. The estimate (in nats) is computed as:
- S_p - sum(nk * log(qk)) / sum(nk)
where S_p is the entropy estimate from counts nk.
Parameters
----------
nk : array_like
The number of occurrences of a set of bins.
qk : array_like
Reference PMF in sum(nk log(nk/qk).
Must be a valid PMF (non-negative, normalized) and len(qk) = len(nk).
estimator : str or entropy estimator instance, optional
If a string, use the estimator class with the same name and default
parameters. Check ndd.entropy_estimators for the available estimators.
Default: use the Nemenman-Shafee-Bialek (NSB) estimator.
Returns
-------
float
Kullback-Leibler divergence.
"""
estimator = as_estimator(estimator)
nk = numpy.asarray(nk)
k = len(qk)
if k == 1: # single bin
return 0.0
return cross_entropy(nk, qk) - estimator.fit(nk, k=k).estimate_
def interaction_information(ar, ks=None, estimator='nsb', axis=0, r=None):
"""Interaction information from data matrix.
See Eq.10 in:
Timme, Nicholas, et al.
"Synergy, redundancy, and multivariate information measures:
an experimentalist's perspective."
Journal of computational neuroscience 36.2 (2014): 119-140.
Paramaters
----------
ar : array-like
n-by-p array of n samples from p discrete variables.
ks : 1D array of length p, optional
Alphabet size for each variable.
estimator : str or entropy estimator instance, optional
If a string, use the estimator class with the same name and default
parameters. Check ndd.entropy_estimators for the available estimators.
Default: Nemenman-Shafee-Bialek (NSB) estimator.
axis : int, optional
The sample-indexing axis. Defaults to 0.
r : int, optional; 1<=r<=p.
If passed, return a generator yielding estimates for the p-choose-r
possible combinations of r variables.
Combinations are ordered as: list(itertools.combinations(range(p), r)).
Returns
-------
float
Interaction information estimate.
Raises
------
CardinalityError
If len(ks) != p.
"""
def iinfo(X, ks, estimator):
"""Helper function for interaction information definition.
Ref: timme2014synergy
"""
info = 0.0
S = len(X)
for T in range(1, S + 1):
sgn = (-1)**(S - T)
info += sgn * sum(from_data(X, ks=ks, estimator=estimator, r=T))
return -info
estimator = as_estimator(estimator)
if not isinstance(ar, DataArray):
ar = DataArray(ar, ks=ks, axis=axis)
if r is not None:
return estimates_from_combinations(ar, r, q=iinfo, estimator=estimator)
data, k = ar.iter_data()
return iinfo(data, k, estimator)
def mutual_information(ar, ks=None, estimator='nsb', axis=0):
"""Mutual information from p-by-n data matrix.
If p > 2, return an estimate of the mutual information for each possible
pair of variables, ordered as list(itertools.combinations(range(p), r=2)).
Paramaters
----------
ar : array-like
n-by-p array of n samples from p discrete variables.
ks : 1D p-dimensional array, optional
Alphabet size for each variable.
estimator : str or entropy estimator instance, optional
If a string, use the estimator class with the same name and default
parameters. Check ndd.entropy_estimators for the available estimators.
Default: use the Nemenman-Shafee-Bialek (NSB) estimator.
axis : int, optional
The sample-indexing axis. Defaults to 0.
Returns
-------
float
Coinformation estimate.
Raises
------
CardinalityError
If len(ks) != p.
"""
estimator = as_estimator(estimator)
if not isinstance(ar, DataArray):
ar = DataArray(ar, ks=ks, axis=axis)
p = ar.shape[0]
# entropies for single fearures
h1 = list(from_data(ar, r=1, estimator=estimator))
if p > 2:
def mi_for_all_pairs():
"""Yield the mutual info for all pairs of features."""
for i1, i2 in combinations(range(p), 2):
yield h1[i1] + h1[i2] - from_data(ar[i1, i2],
estimator=estimator)
return mi_for_all_pairs()
return h1[0] + h1[1] - from_data(ar, estimator=estimator)
def estimates_from_combinations(ar,
r,
*,
q=from_data,
estimator='nsb',
subset=None):
"""Apply the estimator function `func` to combinations of data features.
Parameters
----------
ar : array-like
p-by-n data array.
r : int, optional; ; 1<=r<=p.
Length of feature combinations.
q : callable, optional
A callable returning the quantity to be estimated from data
estimator : str or entropy estimator instance, optional
If a string, use the estimator class with the same name and default
parameters. Check ndd.entropy_estimators for the available estimators.
Default: Nemenman-Shafee-Bialek (NSB) estimator.
subset : list, optional
Return only the results for combinations of features that contain
the `subset` of features.
Yields
------
estimate : float
"""
estimator = as_estimator(estimator)
if not isinstance(ar, DataArray):
ar = DataArray(ar)
p = ar.shape[0]
feature_combinations = zip(combinations(range(p), r), ar.iter_data(r=r))
if subset is not None:
subset = set(subset)
for ids, (x, k) in feature_combinations:
if subset <= set(ids):
yield q(x, k, estimator=estimator)
else:
for ids, (x, k) in feature_combinations:
yield q(x, k, estimator=estimator)
def jensen_shannon_divergence(nk, k=None, estimator='Nsb'):
"""
Jensen-Shannon divergence from a m-by-p matrix of counts.
Return an estimate of the Jensen-Shannon divergence between
m unknown discrete distributions from a m-by-p input array of counts.
The estimate (in nats) is computed as a combination of single Bayesian
entropy estimates. If the total number of samples varies among the
distributions, use a weighted average (see the general definition of
the Jensen-Shannon divergence:
https://en.wikipedia.org/wiki/Jensen-Shannon_divergence).
Parameters
----------
nk : array-like, shape (m, p)
Matrix of frequency counts. Each row corresponds to the number of
occurrences of a set of bins from a different distribution.
k : int or array-like, optional
Total number of bins (including unobserved bins); k >= p.
A float is a valid input for whole numbers (e.g. k=1.e3).
If an array, set k = numpy.prod(k). Defaults to p.
estimator : str or entropy estimator instance, optional
If a string, use the estimator class with the same name and default
parameters. Check ndd.entropy_estimators for the available estimators.
Default: use the Nemenman-Shafee-Bialek (NSB) estimator.
Returns
-------
float
Jensen-Shannon divergence.
"""
estimator = as_estimator(estimator)
estimator = JsDivergence(estimator).fit(nk, k=k)
js = estimator.estimate_
if numpy.isnan(js):
logger.warning('nan value for JS divergence')
js = numpy.nan
return js
def from_data(ar, ks=None, estimator='nsb', axis=0, r=None):
"""
Entropy estimate from data matrix.
Paramaters
----------
ar : array-like, shape (n, p)
2D array of n samples from p discrete variables.
ks : int or 1D array of length p, optional
Alphabet size for each variable.
If int, the variables share the same alphabet size.
estimator : str or entropy estimator instance, optional
If a string, use the estimator class with the same name and default
parameters. Check ndd.entropy_estimators for the available estimators.
Default: Nemenman-Shafee-Bialek (NSB) estimator.
axis : int, optional
The sample-indexing axis. Defaults to 0.
r : int, optional; ; 1<=r<=p.
If passed, return a generator yielding estimates for the p-choose-r
possible combinations of r variables.
Returns
-------
float
Entropy estimate
"""
estimator = as_estimator(estimator)
if not isinstance(ar, DataArray):
ar = DataArray(ar, ks=ks, axis=axis)
if r is not None:
return estimates_from_combinations(ar, r, estimator=estimator)
counts, k = ar.iter_counts()
return estimator(counts, k=k)
def conditional_entropy(ar, c, ks=None, estimator='nsb', axis=0, r=None): # pylint: disable=too-many-arguments
"""
Coditional entropy estimate from data matrix.
Paramaters
----------
ar : array-like
n-by-p array of n samples from p discrete variables.
c : int or array-like
The variables on which entropy is conditioned (as column indices).
ks : 1D p-dimensional array, optional
Alphabet size for each variable.
estimator : str or entropy estimator instance, optional
If a string, use the estimator class with the same name and default
parameters. Check ndd.entropy_estimators for the available estimators.
Default: use the Nemenman-Shafee-Bialek (NSB) estimator.
axis : int, optional
The sample-indexing axis. Defaults to 0.
r : int or None, optional; 1<=r<=p-len(c).
If passed, return a generator yielding estimates for all possible
combinations of r variables conditioning on the `c` variables.
Indices are sorted as:
list(x for x in collections.combinations(range(p), r=r+len(c))
if set(c) <= set(x))
Returns
-------
float
Conditional entropy estimate
"""
# TODO: add tests if r is not None
# check data shape
if not isinstance(ar, DataArray):
ar = DataArray(ar, ks=ks, axis=axis)
p = ar.shape[0]
try:
c = list(c)
except TypeError:
c = [c]
if not set(c) <= set(range(p)):
return EstimatorInputError('The indices of conditioning variables'
' are not valid')
# EntropyEstimator objects are callable and return the fitted estimate
estimator = as_estimator(estimator)
# Entropy of features on which we are conditioning
counts, kc = ar[c].iter_counts()
hc = estimator(counts, k=kc)
def centropy(x, k, estimator):
"""Helper function for conditional entropy."""
return from_data(x, ks=k, estimator=estimator) - hc
if r is not None:
# r should be >= p - len(c)
# include the c variables in the set
r = r + len(c)
return estimates_from_combinations(ar,
r,
q=centropy,
estimator=estimator,
subset=c)
_, k = ar.iter_data()
return centropy(ar, k, estimator)
def entropy(nk, *, k=None, estimator=None, return_std=False):
"""
Bayesian Entropy estimate from an array of counts.
The `entropy` function takes as input a vector of frequency counts `nk`
(the observed frequencies for a set of classes or states) and an alphabet
size `k` (the number of classes with non-zero probability, including
unobserved classes) and returns an entropy estimate (in nats) computed
using the Nemenman-Schafee-Bialek (NSB) algorithm.
>>> import ndd
>>> counts = [4, 12, 4, 5, 3, 1, 5, 1, 2, 2, 2, 2, 11, 3, 4, 12, 12, 1, 2]
>>> ndd.entropy(counts, k=100)
2.8060922529931225
The uncertainty in the entropy estimate can be quantified using the
posterior standard deviation (see Eq. 13 in Archer 2013:
https://pillowlab.princeton.edu/pubs/Archer13_MIestim_Entropy.pdf
>>> ndd.entropy(counts, k=100, return_std=True)
(2.8060922529931225, 0.11945501149743358)
If the alphabet size is unknown or countably infinite, the `k` argument
can be omitted and the function will either use an upper bound
estimate for `k` or switch to the asymptotic NSB estimator for strongly
undersampled distributions (see Equations 29, 30 in Nemenman2011:
https://nemenmanlab.org/~ilya/images/c/c1/Nemenman_2011b.pdf)
>>> import ndd
>>> counts = [4, 12, 4, 5, 3, 1, 5, 1, 2, 2, 2, 2, 11, 3, 4, 12, 12, 1, 2]
>>> ndd.entropy(counts) # k is omitted
2.8130746489179046
When the alphabet size is unknown and no coincidences (no bins with
frequency > 1) can be found in the counts array, no entropy estimator can
give a reasonable estimate. In this case, the function returns the
logarithm of the number of samples, and the error is set to inf.
>>> counts = [1]*100
>>> ndd.entropy(counts, return_std=True)
(4.605170185988092, inf)
Parameters
----------
nk : array-like or dict or tuple
The number of occurrences of a set of bins. If a dictionary
use the dictionary values `nk.values()` as counts.
If normalized, take `nk` as a PMF and return the corresponding entropy.
If `nk` is a tuple of two arrays, these correspond respectively to
the set of unique counts values and the number of times each unique
value comes up in the counts array (multiplicities representation).
k : int or array-like, optional
Alphabet size (the number of bins with non-zero probability).
If an array, set k = numpy.prod(k).
Default: use an upper bound estimate for the alphabet size. If the
distribution is strongly undersampled, switch to the asymptotic NSB
estimator that can be used even if the alphabet size is unknown.
estimator : str or entropy estimator obj, optional
Enforce a specific estimator. Check `ndd.entropy_estimators` for
available estimators. Default: use the NSB estimator (or the zeroth
order approximation discussed in Nemenman2011 if the distribution is
strongly undersampled).
return_std : boolean, optional
If True, also return the standard deviation over the entropy posterior.
Returns
-------
entropy : float
Entropy estimate.
err : float, optional
Bayesian error bound on the entropy estimate.
Only if `return_std` is True.
Notes
-----
After a call, the fitted parameters can be inspected checking the
`entropy.info` dictionary:
>>> import ndd
>>> counts = [4, 12, 4, 5, 3, 1, 5, 1, 2, 2, 2, 2, 11, 3, 4, 12, 12, 1, 2]
>>> ndd.entropy(counts)
2.8130746489179046
>>> ndd.entropy.info
{'entropy': 2.8130746489179046, 'err': 0.1244390183672502, 'bounded': 1, 'estimator': 'Nsb(alpha=None)', 'k': 6008}
`entropy.info['bounded']` is equal to 1 if the entropy estimate has error
bounds, 0 when the estimate is unbounded (when no coincidences have
occurred in the data).
"""
if isinstance(nk, tuple) and len(nk) == 2:
nk, zk = nk
else:
nk = as_counts_array(nk)
pk = nk
nk, zk = CountsDistribution().fit(nk).multiplicities
if estimator is None:
estimator = AutoEstimator()
else:
estimator = as_estimator(estimator)
estimator = estimator.fit(nk=nk, zk=zk, k=k)
S, err = estimator.estimate_, estimator.err_
if S is not None and numpy.isnan(S):
# happens if 0 <= pk <= 1
# (possibly unnormalized) pmf
pk_sum = pk.sum()
if pk_sum > 0 and isinstance(estimator, AutoEstimator):
nk = pk / pk_sum
estimator = PmfPlugin().fit(nk=nk)
S, err = estimator.estimate_, estimator.err_
else:
logger.warning('nan value for entropy estimate')
# annotate the entropy function
entropy.info = {}
entropy.info['entropy'] = S
entropy.info['err'] = err
entropy.info['bounded'] = int(err is not None and numpy.isfinite(err))
if isinstance(estimator, AutoEstimator):
entropy.info['estimator'] = str(estimator.estimator)
entropy.info['k'] = estimator.k
else:
entropy.info['estimator'] = str(estimator)
entropy.info['k'] = k
if return_std:
if err is not None and numpy.isnan(err):
logger.warning('nan value for entropy posterior std deviation')
return S, err
return S
