matplotlib example getprobs (snippet)

Python matplotlib example 'getprobs'

Functions in program:

• def _get_probs(nobs):
• def sigFigs(x, n, expthresh=5, pval=False):

Modules used in program:

• import matplotlib.pyplot as plt
• import matplotlib
• import numpy as np

python getprobs

Python matplotlib example: getprobs

import numpy as np

import matplotlib
from matplotlib.transforms import Transform
from matplotlib.scale import ScaleBase
from matplotlib.ticker import (
    FixedLocator,
    NullLocator,
    Formatter,
    NullFormatter,
    FuncFormatter
)
import matplotlib.pyplot as plt
from scipy import stats 

%matplotlib inline

def sigFigs(x, n, expthresh=5, pval=False):
    '''
    Formats a number into a string with the correct number of sig figs.

    Input:
        x (numeric) : the number you want to round
        n (int) : the number of sig figs it should have

    Typical Usage:
        >>> print(sigFigs(1247.15, 3))
               1250
        >>> print(sigFigs(1247.15, 7))
               1247.150
    '''
    # check on the number provided
    if x is not None and not np.isinf(x) and not np.isnan(x):

        # check on the sigFigs
        if n < 1:
            raise ValueError("number of sig figs must be greater than zero!")

        # return a string value unaltered
        #if type(x) == types.StringType:
        if isinstance(x, str):
            out = x

        # logic to do all of the rounding
        elif x != 0.0:
            order = np.floor(np.log10(np.abs(x)))

            if -1.0 * expthresh <= order <= expthresh:
                decimal_places = int(n - 1 - order)

                if decimal_places <= 0:
                    out = '{0:,.0f}'.format(round(x, decimal_places))

                else:
                    fmt = '{0:,.%df}' % decimal_places
                    out = fmt.format(x)

            else:
                decimal_places = n - 1
                fmt = '{0:.%de}' % decimal_places
                out = fmt.format(x)

        else:
            out = str(round(x, n))

    # with NAs and INFs, just return 'NA'
    else:
        out = 'NA'

    return out


def _get_probs(nobs):
    '''Returns the x-axis labels for a probability plot based
    on the number of observations (`nobs`)
    '''
    order = int(np.floor(np.log10(nobs)))
    base_probs = np.array([10, 20, 30, 40, 50, 60, 70, 80, 90])

    axis_probs = base_probs.copy()
    for n in range(order):
        if n <= 2:
            lower_fringe = np.array([1, 2, 5])
            upper_fringe = np.array([5, 8, 9])
        else:
            lower_fringe = np.array([1])
            upper_fringe = np.array([9])

        new_lower = lower_fringe/10**(n)
        new_upper = upper_fringe/10**(n) + axis_probs.max()
        axis_probs = np.hstack([new_lower, axis_probs, new_upper])

    return axis_probs

class ProbTransform(Transform):
    input_dims = 1
    output_dims = 1
    is_separable = True
    has_inverse = True

    def __init__(self, dist):
        Transform.__init__(self)
        self.dist = dist

    def transform_non_affine(self, a):
        return self.dist.ppf(a / 100.)

    def inverted(self):
        return InvertedProbTransform(self.dist)


class InvertedProbTransform(Transform):
    input_dims = 1
    output_dims = 1
    is_separable = True
    has_inverse = True

    def __init__(self):
        self.dist = dist
        Transform.__init__(self)

    def transform_non_affine(self, a):
        return self.dist.cdf(a) * 100.

    def inverted(self):
        return ProbTransform()


class ProbScale(ScaleBase):
    """
    A standard logarithmic scale.  Care is taken so non-positive
    values are not plotted.

    For computational efficiency (to push as much as possible to Numpy
    C code in the common cases), this scale provides different
    transforms depending on the base of the logarithm:

    """
    name = 'prob'


    def __init__(self, axis, **kwargs):
        self.dist = kwargs.pop('dist', stats.norm)
        self._transform = ProbTransform(self.dist)


    def set_default_locators_and_formatters(self, axis):
        """
        Set the locators and formatters to specialized versions for
        log scaling.
        """
        axis.set_major_locator(FixedLocator(_get_probs(1e8)))
        axis.set_major_formatter(FuncFormatter(ProbFormatter()))
        axis.set_minor_locator(NullLocator())
        axis.set_minor_formatter(NullFormatter())

    def get_transform(self):
        """
        Return a :class:`~matplotlib.transforms.Transform` instance
        appropriate for the given logarithm base.
        """
        return self._transform

    def limit_range_for_scale(self, vmin, vmax, minpos):
        """
        Limit the domain to positive values.
        """
        return (vmin <= 0.0 and minpos or vmin,
                vmax <= 0.0 and minpos or vmax)


class ProbFormatter(Formatter):
    def __call__(self, x, pos=None):
        if x < 10:
            out = sigFigs(x, 1)
        elif x <= 99:
            out =  sigFigs(x, 2)
        else:
            order = np.ceil(np.abs(np.log10(100 - x)))
            out = sigFigs(x, order + 2)

        return '{}'.format(out)

if __name__ == '__main__':    
    matplotlib.scale.register_scale(ProbScale)
    x = np.arange(0.001, 99.999, 0.01)
    y = np.random.normal(loc=2, scale=0.75, size=x.shape)
    y.sort()

    mydist = stats.norm

    fig, ax = plt.subplots(figsize=(20, 4))
    ax.plot(x, y)
    ax.set_xscale('prob', dist=mydist)
    t = plt.xticks(rotation=90)

Python links

• Learn Python: https://pythonbasics.org/
• Python Tutorial: https://pythonprogramminglanguage.com