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Pearson’s Contingency Coefficient

Module Interface

class torchmetrics.nominal.PearsonsContingencyCoefficient(num_classes, nan_strategy='replace', nan_replace_value=0.0, **kwargs)[source]

Compute Pearson’s Contingency Coefficient statistic.

This metric measures the association between two categorical (nominal) data series.

\[Pearson = \sqrt{\frac{\chi^2 / n}{1 + \chi^2 / n}}\]

where

\[\chi^2 = \sum_{i,j} \ frac{\left(n_{ij} - \frac{n_{i.} n_{.j}}{n}\right)^2}{\frac{n_{i.} n_{.j}}{n}}\]

where \(n_{ij}\) denotes the number of times the values \((A_i, B_j)\) are observed with \(A_i, B_j\) represent frequencies of values in preds and target, respectively. Pearson’s Contingency Coefficient is a symmetric coefficient, i.e. \(Pearson(preds, target) = Pearson(target, preds)\), so order of input arguments does not matter. The output values lies in [0, 1] with 1 meaning the perfect association.

As input to forward and update the metric accepts the following input:

  • preds (Tensor): Either 1D or 2D tensor of categorical (nominal) data from the first data series with shape (batch_size,) or (batch_size, num_classes), respectively.

  • target (Tensor): Either 1D or 2D tensor of categorical (nominal) data from the second data series with shape (batch_size,) or (batch_size, num_classes), respectively.

As output of forward and compute the metric returns the following output:

  • pearsons_cc (Tensor): Scalar tensor containing the Pearsons Contingency Coefficient statistic.

Parameters:
  • num_classes (int) – Integer specifing the number of classes

  • nan_strategy (Literal['replace', 'drop']) – Indication of whether to replace or drop NaN values

  • nan_replace_value (Union[int, float, None]) – Value to replace NaN``s when ``nan_strategy = 'replace'

  • kwargs (Any) – Additional keyword arguments, see Advanced metric settings for more info.

Raises:
  • ValueError – If nan_strategy is not one of ‘replace’ and ‘drop’

  • ValueError – If nan_strategy is equal to ‘replace’ and nan_replace_value is not an int or float

Example:

>>> from torchmetrics.nominal import PearsonsContingencyCoefficient
>>> _ = torch.manual_seed(42)
>>> preds = torch.randint(0, 4, (100,))
>>> target = torch.round(preds + torch.randn(100)).clamp(0, 4)
>>> pearsons_contingency_coefficient = PearsonsContingencyCoefficient(num_classes=5)
>>> pearsons_contingency_coefficient(preds, target)
tensor(0.6948)
plot(val=None, ax=None)[source]

Plot a single or multiple values from the metric.

Parameters:
  • val (Union[Tensor, Sequence[Tensor], None]) – Either a single result from calling metric.forward or metric.compute or a list of these results. If no value is provided, will automatically call metric.compute and plot that result.

  • ax (Optional[Axes]) – An matplotlib axis object. If provided will add plot to that axis

Return type:

Tuple[Figure, Union[Axes, ndarray]]

Returns:

Figure and Axes object

Raises:

ModuleNotFoundError – If matplotlib is not installed

>>> # Example plotting a single value
>>> import torch
>>> from torchmetrics.nominal import PearsonsContingencyCoefficient
>>> metric = PearsonsContingencyCoefficient(num_classes=5)
>>> metric.update(torch.randint(0, 4, (100,)), torch.randint(0, 4, (100,)))
>>> fig_, ax_ = metric.plot()
../_images/pearsons_contingency_coefficient-1.png
>>> # Example plotting multiple values
>>> import torch
>>> from torchmetrics.nominal import PearsonsContingencyCoefficient
>>> metric = PearsonsContingencyCoefficient(num_classes=5)
>>> values = [ ]
>>> for _ in range(10):
...     values.append(metric(torch.randint(0, 4, (100,)), torch.randint(0, 4, (100,))))
>>> fig_, ax_ = metric.plot(values)
../_images/pearsons_contingency_coefficient-2.png

Functional Interface

torchmetrics.functional.nominal.pearsons_contingency_coefficient(preds, target, nan_strategy='replace', nan_replace_value=0.0)[source]

Compute Pearson’s Contingency Coefficient for measuring the association between two categorical data series.

\[Pearson = \sqrt{\frac{\chi^2 / n}{1 + \chi^2 / n}}\]

where

\[\chi^2 = \sum_{i,j} \ frac{\left(n_{ij} - \frac{n_{i.} n_{.j}}{n}\right)^2}{\frac{n_{i.} n_{.j}}{n}}\]

where \(n_{ij}\) denotes the number of times the values \((A_i, B_j)\) are observed with \(A_i, B_j\) represent frequencies of values in preds and target, respectively.

Pearson’s Contingency Coefficient is a symmetric coefficient, i.e. \(Pearson(preds, target) = Pearson(target, preds)\).

The output values lies in [0, 1] with 1 meaning the perfect association.

Parameters:
  • preds (Tensor) –

    1D or 2D tensor of categorical (nominal) data:

    • 1D shape: (batch_size,)

    • 2D shape: (batch_size, num_classes)

  • target (Tensor) –

    1D or 2D tensor of categorical (nominal) data:

    • 1D shape: (batch_size,)

    • 2D shape: (batch_size, num_classes)

  • nan_strategy (Literal['replace', 'drop']) – Indication of whether to replace or drop NaN values

  • nan_replace_value (Union[int, float, None]) – Value to replace NaN``s when ``nan_strategy = 'replace'

Return type:

Tensor

Returns:

Pearson’s Contingency Coefficient

Example

>>> from torchmetrics.functional.nominal import pearsons_contingency_coefficient
>>> _ = torch.manual_seed(42)
>>> preds = torch.randint(0, 4, (100,))
>>> target = torch.round(preds + torch.randn(100)).clamp(0, 4)
>>> pearsons_contingency_coefficient(preds, target)
tensor(0.6948)

pearsons_contingency_coefficient_matrix

torchmetrics.functional.nominal.pearsons_contingency_coefficient_matrix(matrix, nan_strategy='replace', nan_replace_value=0.0)[source]

Compute Pearson’s Contingency Coefficient statistic between a set of multiple variables.

This can serve as a convenient tool to compute Pearson’s Contingency Coefficient for analyses of correlation between categorical variables in your dataset.

Parameters:
  • matrix (Tensor) –

    A tensor of categorical (nominal) data, where:

    • rows represent a number of data points

    • columns represent a number of categorical (nominal) features

  • nan_strategy (Literal['replace', 'drop']) – Indication of whether to replace or drop NaN values

  • nan_replace_value (Union[int, float, None]) – Value to replace NaN``s when ``nan_strategy = 'replace'

Return type:

Tensor

Returns:

Pearson’s Contingency Coefficient statistic for a dataset of categorical variables

Example

>>> from torchmetrics.functional.nominal import pearsons_contingency_coefficient_matrix
>>> _ = torch.manual_seed(42)
>>> matrix = torch.randint(0, 4, (200, 5))
>>> pearsons_contingency_coefficient_matrix(matrix)
tensor([[1.0000, 0.2326, 0.1959, 0.2262, 0.2989],
        [0.2326, 1.0000, 0.1386, 0.1895, 0.1329],
        [0.1959, 0.1386, 1.0000, 0.1840, 0.2335],
        [0.2262, 0.1895, 0.1840, 1.0000, 0.2737],
        [0.2989, 0.1329, 0.2335, 0.2737, 1.0000]])
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