elapid.stats

Utilities for calculating zonal stats and other transformations

RasterStat

Utility class to iterate over and apply reductions to multiband arrays

Source code in elapid/stats.py

class RasterStat:
    """Utility class to iterate over and apply reductions to multiband arrays"""

    def __init__(self, name: str, method: Callable, dtype: str = None, **kwargs):
        """Create a RasterStat object

        Args:
            name: the label to prepend to the output column
            method: function to reduce a 2d ndarray to an (nbands,) shape array
            dtype: the output array data type
            **kwargs: additional arguments to pass to `method`
        """
        self.name = name
        self.method = method
        self.dtype = dtype
        self.kwargs = kwargs

    def format(self, x: np.ndarray) -> np.ndarray:
        """Format the array data into an array of shape [nbands, n_valid_pixels]

        Args:
            x: ndarray of shape (nbands, nrows, ncols) or (nbands, n_valid_pixels)

        Returns:
            2d ndarray
        """
        if x.ndim == 3:
            bands, rows, cols = x.shape
            x = x.reshape((bands, rows * cols))
        return x

    def reduce(self, x: np.ndarray) -> np.ndarray:
        """Reduce an array using the objects `method` function

        Args:
            x: ndarray of shape (nbands, n_valid_pixels)

        Returns:
            ndarray of shape (nbands,)
        """
        return self.method(self.format(x), **self.kwargs)

__init__(name, method, dtype=None, **kwargs)

Create a RasterStat object

Parameters:

Name	Type	Description	Default
name	str	the label to prepend to the output column	required
method	Callable	function to reduce a 2d ndarray to an (nbands,) shape array	required
dtype	str	the output array data type	None
**kwargs		additional arguments to pass to method	{}

Source code in elapid/stats.py

def __init__(self, name: str, method: Callable, dtype: str = None, **kwargs):
    """Create a RasterStat object

    Args:
        name: the label to prepend to the output column
        method: function to reduce a 2d ndarray to an (nbands,) shape array
        dtype: the output array data type
        **kwargs: additional arguments to pass to `method`
    """
    self.name = name
    self.method = method
    self.dtype = dtype
    self.kwargs = kwargs

format(x)

Format the array data into an array of shape [nbands, n_valid_pixels]

Parameters:

Name	Type	Description	Default
x	np.ndarray	ndarray of shape (nbands, nrows, ncols) or (nbands, n_valid_pixels)	required

Returns:

Type	Description
np.ndarray	2d ndarray

Source code in elapid/stats.py

def format(self, x: np.ndarray) -> np.ndarray:
    """Format the array data into an array of shape [nbands, n_valid_pixels]

    Args:
        x: ndarray of shape (nbands, nrows, ncols) or (nbands, n_valid_pixels)

    Returns:
        2d ndarray
    """
    if x.ndim == 3:
        bands, rows, cols = x.shape
        x = x.reshape((bands, rows * cols))
    return x

reduce(x)

Reduce an array using the objects method function

Parameters:

Name	Type	Description	Default
x	np.ndarray	ndarray of shape (nbands, n_valid_pixels)	required

Returns:

Type	Description
np.ndarray	ndarray of shape (nbands,)

Source code in elapid/stats.py

def reduce(self, x: np.ndarray) -> np.ndarray:
    """Reduce an array using the objects `method` function

    Args:
        x: ndarray of shape (nbands, n_valid_pixels)

    Returns:
        ndarray of shape (nbands,)
    """
    return self.method(self.format(x), **self.kwargs)

get_raster_stats_methods(mean=True, min=False, max=False, count=False, sum=False, stdv=False, skew=False, kurtosis=False, mode=False, percentiles=[], all=False)

Return RasterStat configs for the requested stats calculations

Source code in elapid/stats.py

def get_raster_stats_methods(
    mean: bool = True,
    min: bool = False,
    max: bool = False,
    count: bool = False,
    sum: bool = False,
    stdv: bool = False,
    skew: bool = False,
    kurtosis: bool = False,
    mode: bool = False,
    percentiles: list = [],
    all: bool = False,
) -> List[RasterStat]:
    """Return RasterStat configs for the requested stats calculations"""
    methods = []

    if mean or all:
        methods.append(RasterStat(name="mean", method=raster_mean, dtype="float32"))

    if min or all:
        methods.append(RasterStat(name="min", method=raster_min))

    if max or all:
        methods.append(RasterStat(name="max", method=raster_max))

    if count or all:
        methods.append(RasterStat(name="count", method=raster_count, dtype="int16"))

    if sum or all:
        methods.append(RasterStat(name="sum", method=raster_sum))

    if stdv or all:
        methods.append(RasterStat(name="stdv", method=raster_stdv))

    if skew or all:
        methods.append(RasterStat(name="skew", method=raster_skew))

    if kurtosis or all:
        methods.append(RasterStat(name="kurt", method=raster_kurtosis))

    if mode or all:
        methods.append(RasterStat(name="mode", method=raster_mode))

    if len(percentiles) > 0:
        for percentile in percentiles:
            methods.append(RasterStat(name=f"{percentile}pct", method=raster_percentile, pctile=percentile))

    return methods

normalize_sample_probabilities(values)

Compute scaled probability scores for an array of samples.

These normalized probabilities sum to 1.0 and are designed to be used as the p parameter for determining sample probabilities in np.random.choice

Parameters:

Name	Type	Description	Default
values	ArrayLike	numeric array to be treated as sample probabilities. probabilities will be scaled linearly based on the input range. setting values = np.array([2, 1, 1]) returns (0.5, 0.25, 0.25)	required

Returns:

Type	Description
np.ndarray	sample probabiility scores

Source code in elapid/stats.py

def normalize_sample_probabilities(values: ArrayLike) -> np.ndarray:
    """Compute scaled probability scores for an array of samples.

    These normalized probabilities sum to 1.0 and are designed to be used
        as the `p` parameter for determining sample probabilities in
        np.random.choice

    Args:
        values: numeric array to be treated as sample probabilities.
            probabilities will be scaled linearly based on the input range.
            setting `values = np.array([2, 1, 1])` returns (0.5, 0.25, 0.25)

    Returns:
        sample probabiility scores
    """
    return values / np.linalg.norm(values, ord=1)