API Reference¶

class Cdf(Distribution):
    """Represents a Cumulative Distribution Function (CDF)."""

    def copy(self, deep=True):
        """Make a copy.

        Args:
            deep: whether to make a deep copy

        Returns: new Cdf
        """
        return Cdf(self, copy=deep)

    @staticmethod
    def from_seq(seq, normalize=True, sort=True, **options):
        """Make a CDF from a sequence of values.

        Args:
            seq: iterable
            normalize: whether to normalize the Cdf, default True
            sort: whether to sort the Cdf by values, default True
            options: passed to the pd.Series constructor

        Returns: CDF object
        """
        # if normalize==True, normalize AFTER making the Cdf
        # so the last element is exactly 1.0
        pmf = Pmf.from_seq(seq, normalize=False, sort=sort, **options)
        return pmf.make_cdf(normalize=normalize)

    def step(self, **options):
        """Plot the Cdf as a step function.

        Args:
            options: passed to pd.Series.plot
        """
        underride(options, drawstyle="steps-post")
        self.plot(**options)

    def normalize(self):
        """Make the probabilities add up to 1 (modifies self).

        Returns: normalizing constant
        """
        total = self.ps[-1]
        self /= total
        return total

    @property
    def forward(self, **kwargs):
        """Make a function that computes the forward Cdf.

        Args:
            kwargs: keyword arguments passed to interp1d

        Returns: interpolation function from qs to ps
        """

        underride(
            kwargs,
            kind="previous",
            copy=False,
            assume_sorted=True,
            bounds_error=False,
            fill_value=(0, 1),
        )

        interp = interp1d(self.qs, self.ps, **kwargs)
        return interp

    @property
    def inverse(self, **kwargs):
        """Make a function that computes the inverse Cdf.

        Args:
            kwargs: keyword arguments passed to interp1d

        Returns: interpolation function from ps to qs
        """
        underride(
            kwargs,
            kind="next",
            copy=False,
            assume_sorted=True,
            bounds_error=False,
            fill_value=(self.qs[0], np.nan),
        )

        interp = interp1d(self.ps, self.qs, **kwargs)
        return interp

    # calling a Cdf like a function does forward lookup
    __call__ = forward

    # quantile is the same as an inverse lookup
    quantile = inverse

    def median(self):
        """Median (50th percentile).

        Returns: float
        """
        return self.quantile(0.5)

    def make_pmf(self, **kwargs):
        """Make a Pmf from the Cdf.

        Args:
            normalize: Boolean, whether to normalize the Pmf
            kwargs: passed to the Pmf constructor

        Returns: Pmf
        """
        normalize = kwargs.pop("normalize", False)

        diff = np.diff(self, prepend=0)
        pmf = Pmf(diff, index=self.index.copy(), **kwargs)
        if normalize:
            pmf.normalize()
        return pmf

    def make_surv(self, **kwargs):
        """Make a Surv object from the Cdf.

        Args:
            kwargs: passed to the Surv constructor

        Returns: Surv object
        """
        normalize = kwargs.pop("normalize", False)
        total = self.ps[-1]
        surv = Surv(total - self, **kwargs)
        surv.total = total
        if normalize:
            self.normalize()
        return surv

    def make_hazard(self, **kwargs):
        """Make a Hazard from the Cdf.

        Args:
            kwargs: passed to the Hazard constructor

        Returns: Hazard
        """
        pmf = self.make_pmf()
        surv = self.make_surv()
        haz = Hazard(pmf / (pmf + surv), **kwargs)
        haz.total = getattr(surv, "total", 1.0)
        return haz

    def make_same(self, dist):
        """Convert the given dist to Cdf.

        Args:
            dist: Distribution

        Returns: Cdf
        """
        return dist.make_cdf()

    def sample(self, n=1, **kwargs):
        """Sample with replacement using probabilities as weights.

        Uses the inverse CDF.

        Args:
            n: number of values
            **kwargs: passed to interp1d

        Returns: NumPy array
        """
        ps = np.random.random(n)
        return self.inverse(ps, **kwargs)

    def max_dist(self, n):
        """Distribution of the maximum of `n` values from this distribution.

        Args:
            n: integer

        Returns: Cdf
        """
        ps = self**n
        return Cdf(ps, self.index.copy())

    def min_dist(self, n):
        """Distribution of the minimum of `n` values from this distribution.

        Args:
            n: integer

        Returns: Cdf
        """
        ps = 1 - (1 - self) ** n
        return Cdf(ps, self.index.copy())

class Distribution(pd.Series):
    """Parent class of all distribution representations.

    This class inherits from Pandas `Series` and provides
    methods common to all distribution types.
    """

    # total is defined here as a class level variable so it
    # is always available, even if it is not set in an instance
    total = None

    @property
    def qs(self):
        """Get the quantities.

        Returns: NumPy array
        """
        return self.index.values

    @property
    def ps(self):
        """Get the probabilities.

        Returns: NumPy array
        """
        return self.values

    def head(self, n=3):
        """Override Series.head to return a Distribution.

        Args:
            n: number of rows

        Returns: Distribution
        """
        s = super().head(n)
        return self.__class__(s)

    def tail(self, n=3):
        """Override Series.tail to return a Distribution.

        Args:
            n: number of rows

        Returns: Distribution
        """
        s = super().tail(n)
        return self.__class__(s)

    def bar(self, **options):
        """Make a bar plot.

        Note: A previous version of this function used pd.Series.plot.bar,
        but that was a mistake, because that function treats the quantities
        as categorical, even if they are numerical, leading to hilariously
        unexpected results!

        Args:
            options: passed to plt.bar
        """
        underride(options, label=self.name)
        plt.bar(self.qs, self.ps, **options)

    def transform(self, *args, **kwargs):
        """Override to transform the quantities, not the probabilities.

        Args:
            *args: passed to Series.transform
            **kwargs: passed to Series.transform

        Returns: Distribution with the same type as self
        """
        qs = self.index.to_series().transform(*args, **kwargs)
        return self.__class__(self.ps, qs, copy=True)

    def _repr_html_(self):
        """Returns an HTML representation of the series.

        Mostly used for Jupyter notebooks.
        """
        df = pd.DataFrame(dict(probs=self))
        return df._repr_html_()

    def __call__(self, qs):
        """Look up quantities, return counts/probabilities/hazards.

        Args:
            qs: quantity or sequence of quantities

        Returns:
            count/probability/hazard or array of count/probabiliy/hazard
        """
        string_types = (str, bytes, bytearray)

        # if qs is a sequence type, use reindex;
        # otherwise use get
        if hasattr(qs, "__iter__") and not isinstance(qs, string_types):
            s = self.reindex(qs, fill_value=0)
            return s.to_numpy()
        else:
            return self.get(qs, default=0)

    def mean(self):
        """Expected value.

        Returns: float
        """
        return self.make_pmf().mean()

    def mode(self, **kwargs):
        """Most common value.

        If multiple quantities have the maximum probability,
        the first maximal quantity is returned.

        Args:
            kwargs: passed to Series.mode

        Returns: type of the quantities
        """
        return self.make_pmf().mode(**kwargs)

    def var(self):
        """Variance.

        Returns: float
        """
        return self.make_pmf().var()

    def std(self):
        """Standard deviation.

        Returns: float
        """
        return self.make_pmf().std()

    def median(self):
        """Median (50th percentile).

        There are several definitions of median;
        the one implemented here is just the 50th percentile.

        Returns: float
        """
        return self.make_cdf().median()

    def quantile(self, ps, **kwargs):
        """Compute the inverse CDF of ps.

        That is, the quantities that correspond to the given probabilities.

        Args:
            ps: float or sequence of floats
            kwargs: passed to Cdf.quantile

        Returns: float
        """
        return self.make_cdf().quantile(ps, **kwargs)

    def credible_interval(self, p):
        """Credible interval containing the given probability.

        Args:
            p: float 0-1

        Returns: array of two quantities
        """
        tail = (1 - p) / 2
        ps = [tail, 1 - tail]
        return self.quantile(ps)

    def choice(self, size=1, **kwargs):
        """Makes a random selection.

        Uses the probabilities as weights unless `p` is provided.

        Args:
            size: number of values or tuple of dimensions
            kwargs: passed to np.random.choice

        Returns: NumPy array
        """
        pmf = self.make_pmf()
        return pmf.choice(size, **kwargs)

    def sample(self, n, **kwargs):
        """Sample with replacement using probabilities as weights.

        Uses the inverse CDF.

        Args:
            n: number of values
            **kwargs: passed to interp1d

        Returns: NumPy array
        """
        cdf = self.make_cdf()
        return cdf.sample(n, **kwargs)

    def add_dist(self, x):
        """Distribution of the sum of values drawn from self and x.

        Args:
            x: Distribution, scalar, or sequence

        Returns: new Distribution, same subtype as self
        """
        pmf = self.make_pmf()
        res = pmf.add_dist(x)
        return self.make_same(res)

    def sub_dist(self, x):
        """Distribution of the diff of values drawn from self and x.

        Args:
            x: Distribution, scalar, or sequence

        Returns: new Distribution, same subtype as self
        """
        pmf = self.make_pmf()
        res = pmf.sub_dist(x)
        return self.make_same(res)

    def mul_dist(self, x):
        """Distribution of the product of values drawn from self and x.

        Args:
            x: Distribution, scalar, or sequence

        Returns: new Distribution, same subtype as self
        """
        pmf = self.make_pmf()
        res = pmf.mul_dist(x)
        return self.make_same(res)

    def div_dist(self, x):
        """Distribution of the ratio of values drawn from self and x.

        Args:
            x: Distribution, scalar, or sequence

        Returns: new Distribution, same subtype as self
        """
        pmf = self.make_pmf()
        res = pmf.div_dist(x)
        return self.make_same(res)

    def pmf_outer(self, dist, ufunc):
        """Computes the outer product of two PMFs.

        Args:
            dist: Distribution object
            ufunc: function to apply to the qs

        Returns: NumPy array
        """
        pmf = self.make_pmf()
        return pmf.pmf_outer(dist, ufunc)

    def gt_dist(self, x):
        """Probability that a value from self is greater than a value from x.

        Args:
            x: Distribution, scalar, or sequence

        Returns: float probability
        """
        pmf = self.make_pmf()
        return pmf.gt_dist(x)

    def lt_dist(self, x):
        """Probability that a value from self is less than a value from x.

        Args:
            x: Distribution, scalar, or sequence

        Returns: float probability
        """
        pmf = self.make_pmf()
        return pmf.lt_dist(x)

    def ge_dist(self, x):
        """Probability that a value from self is >= than a value from x.

        Args:
            x: Distribution, scalar, or sequence

        Returns: float probability
        """
        pmf = self.make_pmf()
        return pmf.ge_dist(x)

    def le_dist(self, x):
        """Probability that a value from self is <= than a value from x.

        Args:
            x: Distribution, scalar, or sequence

        Returns: float probability
        """
        pmf = self.make_pmf()
        return pmf.le_dist(x)

    def eq_dist(self, x):
        """Probability that a value from self equals a value from x.

        Args:
            x: Distribution, scalar, or sequence

        Returns: float probability
        """
        pmf = self.make_pmf()
        return pmf.eq_dist(x)

    def ne_dist(self, x):
        """Probability that a value from self is <= than a value from x.

        Args:
            x: Distribution, scalar, or sequence

        Returns: float probability
        """
        pmf = self.make_pmf()
        return pmf.ne_dist(x)

    def max_dist(self, n):
        """Distribution of the maximum of `n` values from this distribution.

        Args:
            n: integer

        Returns: Distribution, same type as self
        """
        cdf = self.make_cdf().max_dist(n)
        return self.make_same(cdf)

    def min_dist(self, n):
        """Distribution of the minimum of `n` values from this distribution.

        Args:
            n: integer

        Returns: Distribution, same type as self
        """
        cdf = self.make_cdf().min_dist(n)
        return self.make_same(cdf)

    prob_gt = gt_dist
    prob_lt = lt_dist
    prob_ge = ge_dist
    prob_le = le_dist
    prob_eq = eq_dist
    prob_ne = ne_dist

class Hazard(Distribution):
    """Represents a Hazard function."""

    def copy(self, deep=True):
        """Make a copy.

        Args:
            deep: whether to make a deep copy

        Returns: new Pmf
        """
        return Hazard(self, copy=deep)

    # Hazard inherits __call__ from Distribution

    def normalize(self):
        """Normalize the hazard function (modifies self).

        Returns: normalizing constant
        """
        old_total = getattr(self, "total", 1.0)
        self.total = 1.0
        return old_total

    def make_surv(self, **kwargs):
        """Make a Surv from the Hazard.

        Args:
            kwargs: passed to the Surv constructor

        Returns: Surv
        """
        normalize = kwargs.pop("normalize", False)
        ps = (1 - self).cumprod()
        total = getattr(self, "total", 1.0)
        surv = Surv(ps * total, **kwargs)
        surv.total = total

        if normalize:
            surv.normalize()
        return surv

    def make_cdf(self, **kwargs):
        """Make a Cdf from the Hazard.

        Args:
            kwargs: passed to the Cdf constructor

        Returns: Cdf
        """
        return self.make_surv().make_cdf(**kwargs)

    def make_pmf(self, **kwargs):
        """Make a Pmf from the Hazard.

        Args:
            kwargs: passed to the Pmf constructor

        Returns: Pmf
        """
        return self.make_surv().make_cdf().make_pmf(**kwargs)

    def make_same(self, dist):
        """Convert the given dist to Hazard.

        Args:
            dist: Distribution

        Returns: Hazard
        """
        return dist.make_hazard()

    @staticmethod
    def from_seq(seq, **kwargs):
        """Make a Hazard from a sequence of values.

        Args:
            seq: iterable
            normalize: whether to normalize the Pmf, default True
            sort: whether to sort the Pmf by values, default True
            kwargs: passed to Pmf.from_seq

        Returns: Hazard object
        """
        pmf = Pmf.from_seq(seq, **kwargs)
        return pmf.make_hazard()

class Hist(Pmf):
    """Represents a Pmf that maps from values to frequencies/counts."""

    @staticmethod
    def from_seq(seq, normalize=False, **options):
        """Make a distribution from a sequence of values.

        Args:
            seq: sequence of anything
            normalize: whether to normalize the probabilities
            options: passed along to Pmf

        Returns:  Counter object
        """
        pmf = Pmf.from_seq(seq, normalize=normalize, **options)
        return Hist(pmf, copy=False)

    def _repr_html_(self):
        """Returns an HTML representation of the series.

        Mostly used for Jupyter notebooks.
        """
        df = pd.DataFrame(dict(freqs=self))
        return df._repr_html_()

class Pmf(Distribution):
    """Represents a probability Mass Function (PMF)."""

    def copy(self, deep=True):
        """Make a copy.

        Returns: new Pmf
        """
        return Pmf(self, copy=deep)

    def make_pmf(self, **kwargs):
        """Make a Pmf from the Pmf.

        Returns: Pmf
        """
        if kwargs:
            return Pmf(self, **kwargs)
        return self

    # Pmf overrides the arithmetic operations in order
    # to provide fill_value=0 and return a Pmf.

    def add(self, x, **kwargs):
        """Override add to default fill_value to 0.

        Args:
            x: Distribution, sequence, array, or scalar
            kwargs: passed to Series.add

        Returns: Pmf
        """
        underride(kwargs, fill_value=0)
        s = pd.Series(self, copy=False).add(x, **kwargs)
        return Pmf(s)

    __add__ = add
    __radd__ = add

    def sub(self, x, **kwargs):
        """Override the - operator to default fill_value to 0.

        Args:
            x: Distribution, sequence, array, or scalar
            kwargs: passed to Series.sub

        Returns:  Pmf
        """
        underride(kwargs, fill_value=0)
        s = pd.Series.sub(self, x, **kwargs)
        # s = pd.Series(self, copy=False).sub(self, x, **kwargs)
        return Pmf(s)

    subtract = sub
    __sub__ = sub

    def __rsub__(self, x, **kwargs):
        """Handle reverse subtraction operation.

        Args:
            x: Distribution, sequence, array, or scalar
            kwargs: passed to Series.sub

        Returns: Pmf
        """
        # Reverse the subtraction: x - self
        return Pmf(x).sub(self, **kwargs)

    def mul(self, x, **kwargs):
        """Override the * operator to default fill_value to 0.

        Args:
            x: Distribution, sequence, array, or scalar
            kwargs: passed to Series.mul

        Returns:  Pmf
        """
        underride(kwargs, fill_value=0)
        s = pd.Series(self, copy=False).mul(x, **kwargs)
        return Pmf(s)

    multiply = mul
    __mul__ = mul
    __rmul__ = mul

    def div(self, x, **kwargs):
        """Override the / operator to default fill_value to 0.

        Args:
            x: Distribution, sequence, array, or scalar
            kwargs: passed to Series.div

        Returns:  Pmf
        """
        underride(kwargs, fill_value=0)
        s = pd.Series(self, copy=False).div(x, **kwargs)
        return Pmf(s)

    divide = div
    __truediv__ = div

    def __rtruediv__(self, x, **kwargs):
        """Handle reverse division operation.

        Args:
            x: Distribution, sequence, array, or scalar
            kwargs: passed to Series.div

        Returns:
            Pmf
        """
        # Reverse the division: x / self
        # TODO: Make this work with sequence, array, and scalar
        return Pmf(x).div(self, **kwargs)

    def normalize(self):
        """Make the probabilities add up to 1 (modifies self).

        Returns: float, normalizing constant
        """
        total = self.sum()
        self /= total
        return total

    def mean(self):
        """Computes expected value.

        Returns: float
        """
        if not np.allclose(1, self.sum()):
            raise ValueError("Pmf must be normalized before computing mean")

        if not pd.api.types.is_numeric_dtype(self.dtype):
            raise ValueError("mean is only defined for numeric data")

        return np.sum(self.ps * self.qs)

    def var(self):
        """Variance of a PMF.

        Returns: float
        """
        m = self.mean()
        d = self.qs - m
        return np.sum(d**2 * self.ps)

    def std(self):
        """Standard deviation of a PMF.

        Returns: float
        """
        return np.sqrt(self.var())

    def mode(self, **kwargs):
        """Most common value.

        If multiple quantities have the maximum probability,
        the first maximal quantity is returned.

        Args:
            kwargs: passed to Series.mode

        Returns: type of the quantities
        """
        underride(kwargs, skipna=True)
        return self.idxmax(**kwargs)

    max_prob = mode

    def choice(self, size=1, **kwargs):
        """Makes a random selection.

        Uses the probabilities as weights unless `p` is provided.

        Args:
            size: number of values or tuple of dimensions
            kwargs: passed to np.random.choice

        Returns: NumPy array
        """
        underride(kwargs, p=self.ps)
        return np.random.choice(self.qs, size, **kwargs)

    def add_dist(self, x):
        """Computes the Pmf of the sum of values drawn from self and x.

        Args:
            x: Distribution, scalar, or sequence

        Returns: new Pmf
        """
        if isinstance(x, Distribution):
            return self.convolve_dist(x, np.add.outer)
        else:
            return Pmf(self.ps.copy(), index=self.qs + x)

    def sub_dist(self, x):
        """Computes the Pmf of the diff of values drawn from self and other.

        Args:
            x: Distribution, scalar, or sequence

        Returns: new Pmf
        """
        if isinstance(x, Distribution):
            return self.convolve_dist(x, np.subtract.outer)
        else:
            return Pmf(self.ps.copy(), index=self.qs - x)

    def mul_dist(self, x):
        """Computes the Pmf of the product of values drawn from self and x.

        Args:
            x: Distribution, scalar, or sequence

        Returns: new Pmf
        """
        if isinstance(x, Distribution):
            return self.convolve_dist(x, np.multiply.outer)
        else:
            return Pmf(self.ps.copy(), index=self.qs * x)

    def div_dist(self, x):
        """Computes the Pmf of the ratio of values drawn from self and x.

        Args:
            x: Distribution, scalar, or sequence

        Returns: new Pmf
        """
        if isinstance(x, Distribution):
            return self.convolve_dist(x, np.divide.outer)
        else:
            return Pmf(self.ps.copy(), index=self.qs / x)

    def convolve_dist(self, dist, ufunc):
        """Convolve two distributions.

        Args:
            dist: Distribution
            ufunc: elementwise function for arrays

        Returns: new Pmf
        """
        dist = dist.make_pmf()
        qs = ufunc(self.qs, dist.qs).flatten()
        ps = np.multiply.outer(self.ps, dist.ps).flatten()
        series = pd.Series(ps).groupby(qs).sum()

        return Pmf(series)

    def gt_dist(self, x):
        """Probability that a value from self exceeds a value from x.

        Args:
            x: Distribution object or scalar

        Returns: float probability
        """
        if isinstance(x, Distribution):
            return self.pmf_outer(x, np.greater).sum()
        else:
            return self[self.qs > x].sum()

    def lt_dist(self, x):
        """Probability that a value from self is less than a value from x.

        Args:
            x: Distribution object or scalar

        Returns: float probability
        """
        if isinstance(x, Distribution):
            return self.pmf_outer(x, np.less).sum()
        else:
            return self[self.qs < x].sum()

    def ge_dist(self, x):
        """Probability that a value from self is >= than a value from x.

        Args:
            x: Distribution object or scalar

        Returns: float probability
        """
        if isinstance(x, Distribution):
            return self.pmf_outer(x, np.greater_equal).sum()
        else:
            return self[self.qs >= x].sum()

    def le_dist(self, x):
        """Probability that a value from self is <= than a value from x.

        Args:
            x: Distribution object or scalar

        Returns: float probability
        """
        if isinstance(x, Distribution):
            return self.pmf_outer(x, np.less_equal).sum()
        else:
            return self[self.qs <= x].sum()

    def eq_dist(self, x):
        """Probability that a value from self equals a value from x.

        Args:
            x: Distribution object or scalar

        Returns: float probability
        """
        if isinstance(x, Distribution):
            return self.pmf_outer(x, np.equal).sum()
        else:
            return self[self.qs == x].sum()

    def ne_dist(self, x):
        """Probability that a value from self is <= than a value from x.

        Args:
            x: Distribution object or scalar

        Returns: float probability
        """
        if isinstance(x, Distribution):
            return self.pmf_outer(x, np.not_equal).sum()
        else:
            return self[self.qs != x].sum()

    def pmf_outer(self, dist, ufunc):
        """Computes the outer product of two PMFs.

        Args:
            dist: Distribution object
            ufunc: function to apply to the quantities

        Returns: NumPy array
        """
        dist = dist.make_pmf()
        qs = ufunc.outer(self.qs, dist.qs)
        ps = np.multiply.outer(self.ps, dist.ps)
        return qs * ps

    def make_joint(self, other, **options):
        """Make joint distribution (assuming independence).

        Args:
            other: Pmf
            options: passed to Pmf constructor

        Returns: new Pmf
        """
        qs = pd.MultiIndex.from_product([self.qs, other.qs])
        ps = np.multiply.outer(self.ps, other.ps).flatten()
        return Pmf(ps, index=qs, **options)

    def marginal(self, i, name=None):
        """Gets the marginal distribution of the indicated variable.

        Args:
            i: index of the variable we want
            name: string

        Returns: Pmf
        """
        # The following is deprecated now
        # return Pmf(self.sum(level=i))

        # here's the new version
        return Pmf(self.groupby(level=i).sum(), name=name)

    def conditional(self, i, val, name=None):
        """Gets the conditional distribution of the indicated variable.

        Args:
            i: index of the variable we're conditioning on
            val: the value the ith variable has to have
            name: string

        Returns: Pmf
        """
        pmf = Pmf(self.xs(key=val, level=i), copy=True, name=name)
        pmf.normalize()
        return pmf

    def update(self, likelihood, data):
        """Bayesian update.

        Args:
            likelihood: function that takes (data, hypo) and returns
                        likelihood of data under hypo, P(data|hypo)
            data: in whatever format likelihood understands

        Returns: normalizing constant
        """
        for hypo in self.qs:
            self[hypo] *= likelihood(data, hypo)

        return self.normalize()

    def make_cdf(self, **kwargs):
        """Make a Cdf from the Pmf.

        Args:
            kwargs: passed to the pd.Series constructor

        Returns: Cdf
        """
        normalize = kwargs.pop("normalize", False)

        pmf = self.sort_index()
        cumulative = np.cumsum(pmf)
        cdf = Cdf(cumulative, pmf.index.copy(), **kwargs)

        if normalize:
            cdf.normalize()

        return cdf

    def make_surv(self, **kwargs):
        """Make a Surv from the Pmf.

        Args:
            kwargs: passed to the pd.Series constructor

        Returns: Surv
        """
        cdf = self.make_cdf()
        return cdf.make_surv(**kwargs)

    def make_hazard(self, normalize=False, **kwargs):
        """Make a Hazard from the Pmf.

        Args:
            kwargs: passed to the pd.Series constructor

        Returns: Hazard
        """
        surv = self.make_surv()
        haz = Hazard(self / (self + surv), **kwargs)
        haz.total = getattr(surv, "total", 1.0)
        if normalize:
            self.normalize()
        return haz

    def make_same(self, dist):
        """Convert the given dist to Pmf.

        Args:
            dist: Distribution

        Returns: Pmf
        """
        return dist.make_pmf()

    @staticmethod
    def from_seq(
        seq,
        normalize=True,
        sort=True,
        ascending=True,
        dropna=True,
        na_position="last",
        **options,
    ):
        """Make a PMF from a sequence of values.

        Args:
            seq: iterable
            normalize: whether to normalize the Pmf, default True
            sort: whether to sort the Pmf by values, default True
            ascending: whether to sort in ascending order, default True
            dropna: whether to drop NaN values, default True
            na_position: If 'first' puts NaNs at the beginning,
                        'last' puts NaNs at the end.
        options: passed to the pd.Series constructor

        Returns: Pmf object
        """
        # compute the value counts
        series = pd.Series(seq).value_counts(
            normalize=normalize, sort=False, dropna=dropna
        )
        # make the result a Pmf
        # (since we just made a fresh Series, there is no reason to copy it)
        options["copy"] = False
        underride(options, name="")
        pmf = Pmf(series, **options)

        # sort in place, if desired
        if sort:
            pmf.sort_index(
                inplace=True, ascending=ascending, na_position=na_position
            )

        return pmf