Custom metric in fastai2

Part 1 (2020) Non-beginner
3

Here is my implementation of this metric:

def _accumulate(self, learn):
    #pred = learn.pred.argmax(dim=self.dim_argmax) if self.dim_argmax else learn.pred
    pred = learn.pred
    if self.sigmoid: pred = torch.nn.functional.softmax(pred) #hack for roc_auc_score
    if self.thresh:  pred = (pred >= self.thresh)
    targ = learn.y
    pred,targ = to_detach(pred),to_detach(targ)
    if self.flatten: pred,targ = flatten_check(pred,targ)
    self.preds.append(pred)
    self.targs.append(targ)

AccumMetric.accumulate = _accumulate

def RocAuc(axis=-1, average='macro', sample_weight=None, max_fpr=None,multi_class='ovr'):
    "Area Under the Receiver Operating Characteristic Curve for single-label binary classification problems"
    return skm_to_fastai(skm.roc_auc_score, axis=axis,
                         average=average, sample_weight=sample_weight, max_fpr=max_fpr,flatten=False,multi_class=multi_class,sigmoid=True)
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