TopKCategoricalAccuracy

class ignite.metrics.TopKCategoricalAccuracy(k=5, output_transform=<function TopKCategoricalAccuracy.<lambda>>, device=device(type='cpu'))

Calculates the top-k categorical accuracy.

• update must receive output of the form (y_pred, y) or {'y_pred': y_pred, 'y': y}.

Parameters

• k (int) – the k in “top-k”.

• 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. By default, metrics require the output as (y_pred, y) or {'y_pred': y_pred, 'y': y}.

• 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

To use with Engine and process_function, simply attach the metric instance to the engine. The output of the engine’s process_function needs to be in the format of (y_pred, y) or {'y_pred': y_pred, 'y': y, ...}. If not, output_tranform can be added to the metric to transform the output into the form expected by the metric.

def process_function(engine, batch):
    y_pred, y = batch
    return y_pred, y

def one_hot_to_binary_output_transform(output):
    y_pred, y = output
    y = torch.argmax(y, dim=1)  # one-hot vector to label index vector
    return y_pred, y

engine = Engine(process_function)
metric = TopKCategoricalAccuracy(
    k=2, output_transform=one_hot_to_binary_output_transform)
metric.attach(engine, 'top_k_accuracy')

preds = torch.Tensor([
    [0.7, 0.2, 0.05, 0.05],     # 1 is in the top 2
    [0.2, 0.3, 0.4, 0.1],       # 0 is not in the top 2
    [0.4, 0.4, 0.1, 0.1],       # 0 is in the top 2
    [0.7, 0.05, 0.2, 0.05]      # 2 is in the top 2
])
target = torch.Tensor([         # targets as one-hot vectors
    [0, 1, 0, 0],
    [1, 0, 0, 0],
    [1, 0, 0, 0],
    [0, 0, 1, 0]
])

state = engine.run([[preds, target]])
print(state.metrics['top_k_accuracy'])

0.75

Methods

compute	Computes the metric based on it's accumulated state.
reset	Resets the metric to it's initial state.
update	Updates the metric's state using the passed batch output.

compute()

Computes the metric based on it’s accumulated state.

By default, this is called at the end of each epoch.

Returns

the actual quantity of interest. However, if a Mapping is returned, it will be (shallow) flattened into engine.state.metrics when completed() is called.

Return type

Any

Raises

NotComputableError – raised when the metric cannot be computed.

reset()

Resets the metric to it’s initial state.

By default, this is called at the start of each epoch.

Return type

None

update(output)

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