Precision#

class ignite.metrics.precision.Precision(output_transform=<function _BasePrecisionRecall.<lambda>>, average=False, is_multilabel=False, device=device(type='cpu'))[source]#

Calculates precision for binary, multiclass and multilabel data.

\text{Precision} = \frac{ TP }{ TP + FP }

where $\text{TP}$ is true positives and $\text{FP}$ is false positives.

update must receive output of the form (y_pred, y) or {'y_pred': y_pred, 'y': y}.
y_pred must be in the following shape (batch_size, num_categories, …) or (batch_size, …).
y must be in the following shape (batch_size, …).

Parameters

output_transform (Callable) – a callable that is used to transform the Engine’s process_function’s output into the form expected by the metric. This can be useful if, for example, you have a multi-output model and you want to compute the metric with respect to one of the outputs.
average (Optional[Union[bool, str]]) –
available options are

False
default option. For multicalss and multilabel inputs, per class and per label metric is returned respectively.

None
like False option except that per class metric is returned for binary data as well. For compatibility with Scikit-Learn api.

’micro’
Metric is computed counting stats of classes/labels altogether.

$\text{Micro Precision} = \frac{\sum_{k=1}^C TP_k}{\sum_{k=1}^C TP_k+FP_k}$
where $C$ is the number of classes/labels (2 in binary case). $k$ in $TP_k$ and $FP_k$ means that the measures are computed for class/label $k$ (in a one-vs-rest sense in multiclass case).

For binary and multiclass inputs, this is equivalent with accuracy, so use Accuracy.

’samples’
for multilabel input, at first, precision is computed on a per sample basis and then average across samples is returned.

$\text{Sample-averaged Precision} = \frac{\sum_{n=1}^N \frac{TP_n}{TP_n+FP_n}}{N}$
where $N$ is the number of samples. $n$ in $TP_n$ and $FP_n$ means that the measures are computed for sample $n$ , across labels.

Incompatible with binary and multiclass inputs.

’weighted’
like macro precision but considers class/label imbalance. for binary and multiclass input, it computes metric for each class then returns average of them weighted by support of classes (number of actual samples in each class). For multilabel input, it computes precision for each label then returns average of them weighted by support of labels (number of actual positive samples in each label).

$Precision_k = \frac{TP_k}{TP_k+FP_k}$
$\text{Weighted Precision} = \frac{\sum_{k=1}^C P_k * Precision_k}{N}$
where $C$ is the number of classes (2 in binary case). $P_k$ is the number of samples belonged to class $k$ in binary and multiclass case, and the number of positive samples belonged to label $k$ in multilabel case.

macro
computes macro precision which is unweighted average of metric computed across classes/labels.

$\text{Macro Precision} = \frac{\sum_{k=1}^C Precision_k}{C}$
where $C$ is the number of classes (2 in binary case).

True
like macro option. For backward compatibility.
is_multilabel (bool) – flag to use in multilabel case. By default, value is False.
device (Union[str, device]) – specifies which device updates are accumulated on. Setting the metric’s device to be the same as your update arguments ensures the update method is non-blocking. By default, CPU.

Examples

For more information on how metric works with Engine, visit Attach Engine API.

from collections import OrderedDict

import torch
from torch import nn, optim

from ignite.engine import *
from ignite.handlers import *
from ignite.metrics import *
from ignite.utils import *
from ignite.contrib.metrics.regression import *
from ignite.contrib.metrics import *

# create default evaluator for doctests

def eval_step(engine, batch):
    return batch

default_evaluator = Engine(eval_step)

# create default optimizer for doctests

param_tensor = torch.zeros([1], requires_grad=True)
default_optimizer = torch.optim.SGD([param_tensor], lr=0.1)

# create default trainer for doctests
# as handlers could be attached to the trainer,
# each test must define his own trainer using `.. testsetup:`

def get_default_trainer():

    def train_step(engine, batch):
        return batch

    return Engine(train_step)

# create default model for doctests

default_model = nn.Sequential(OrderedDict([
    ('base', nn.Linear(4, 2)),
    ('fc', nn.Linear(2, 1))
]))

manual_seed(666)

Binary case. In binary and multilabel cases, the elements of y and y_pred should have 0 or 1 values.

metric = Precision()
weighted_metric = Precision(average='weighted')
two_class_metric = Precision(average=None) # Returns precision for both classes
metric.attach(default_evaluator, "precision")
weighted_metric.attach(default_evaluator, "weighted precision")
two_class_metric.attach(default_evaluator, "both classes precision")
y_true = torch.tensor([1, 0, 1, 1, 0, 1])
y_pred = torch.tensor([1, 0, 1, 0, 1, 1])
state = default_evaluator.run([[y_pred, y_true]])
print(f"Precision: {state.metrics['precision']}")
print(f"Weighted Precision: {state.metrics['weighted precision']}")
print(f"Precision for class 0 and class 1: {state.metrics['both classes precision']}")

Precision: 0.75
Weighted Precision: 0.6666666666666666
Precision for class 0 and class 1: tensor([0.5000, 0.7500], dtype=torch.float64)

Multiclass case

metric = Precision()
macro_metric = Precision(average=True)
weighted_metric = Precision(average='weighted')

metric.attach(default_evaluator, "precision")
macro_metric.attach(default_evaluator, "macro precision")
weighted_metric.attach(default_evaluator, "weighted precision")

y_true = torch.tensor([2, 0, 2, 1, 0])
y_pred = torch.tensor([
    [0.0266, 0.1719, 0.3055],
    [0.6886, 0.3978, 0.8176],
    [0.9230, 0.0197, 0.8395],
    [0.1785, 0.2670, 0.6084],
    [0.8448, 0.7177, 0.7288]
])
state = default_evaluator.run([[y_pred, y_true]])
print(f"Precision: {state.metrics['precision']}")
print(f"Macro Precision: {state.metrics['macro precision']}")
print(f"Weighted Precision: {state.metrics['weighted precision']}")

Precision: tensor([0.5000, 0.0000, 0.3333], dtype=torch.float64)
Macro Precision: 0.27777777777777773
Weighted Precision: 0.3333333333333333

Multilabel case, the shapes must be (batch_size, num_labels, …)

metric = Precision(is_multilabel=True)
micro_metric = Precision(is_multilabel=True, average='micro')
macro_metric = Precision(is_multilabel=True, average=True)
weighted_metric = Precision(is_multilabel=True, average='weighted')
samples_metric = Precision(is_multilabel=True, average='samples')

metric.attach(default_evaluator, "precision")
micro_metric.attach(default_evaluator, "micro precision")
macro_metric.attach(default_evaluator, "macro precision")
weighted_metric.attach(default_evaluator, "weighted precision")
samples_metric.attach(default_evaluator, "samples precision")

y_true = torch.tensor([
    [0, 0, 1],
    [0, 0, 0],
    [0, 0, 0],
    [1, 0, 0],
    [0, 1, 1],
])
y_pred = torch.tensor([
    [1, 1, 0],
    [1, 0, 1],
    [1, 0, 0],
    [1, 0, 1],
    [1, 1, 0],
])
state = default_evaluator.run([[y_pred, y_true]])
print(f"Precision: {state.metrics['precision']}")
print(f"Micro Precision: {state.metrics['micro precision']}")
print(f"Macro Precision: {state.metrics['macro precision']}")
print(f"Weighted Precision: {state.metrics['weighted precision']}")
print(f"Samples Precision: {state.metrics['samples precision']}")

Precision: tensor([0.2000, 0.5000, 0.0000], dtype=torch.float64)
Micro Precision: 0.2222222222222222
Macro Precision: 0.2333333333333333
Weighted Precision: 0.175
Samples Precision: 0.2

Thresholding of predictions can be done as below:

def thresholded_output_transform(output):
    y_pred, y = output
    y_pred = torch.round(y_pred)
    return y_pred, y

metric = Precision(output_transform=thresholded_output_transform)
metric.attach(default_evaluator, "precision")
y_true = torch.tensor([1, 0, 1, 1, 0, 1])
y_pred = torch.tensor([0.6, 0.2, 0.9, 0.4, 0.7, 0.65])
state = default_evaluator.run([[y_pred, y_true]])
print(state.metrics["precision"])

0.75

Changed in version 0.4.10: Some new options were added to average parameter.

Methods

update

Updates the metric's state using the passed batch output.

update(output)[source]#

Updates the metric’s state using the passed batch output.

By default, this is called once for each batch.

Parameters: output (Sequence[Tensor]) – the is the output from the engine’s process function.
Return type: None