Hello,

I implemented F1_Score by myself instead of using sklearn. **But** in the validation phase and testing phase, it appears **nan** value. I cannot fix the bug, could you please give me some advice? I will very appreciate it!

I’m working on a multi-class segmentation task.

```
def _get_stat(self, logits, target, nb_classes):
with torch.no_grad():
pred = torch.argmax(logits, dim=1).view(-1)
target = target.view(-1)
pixel_counter = torch.zeros(nb_classes).to(logits.device)
acc = torch.zeros(nb_classes).to(logits.device)
f1 = torch.zeros(nb_classes).to(logits.device)
for k in range(0, nb_classes):
# tp + fp
pred_inds = pred == k
# tp + tn
target_inds = target == k
# tn + fn
non_pred_inds = pred != k
# tn + fp
non_target_inds = target != k
# tp
interection = pred_inds[target_inds].long().sum().float()
# tn
non_interection = non_pred_inds[non_target_inds].long().sum().float()
# fn + fp
denominator = non_pred_inds.long().sum().float() + non_target_inds.long().sum().float() - 2*non_interection
pixel_counter[k] = target_inds.long().sum().float()
acc[k] = interection
f1[k] = ((2 * interection) / (2 * interection + denominator + 1e-10))
return (acc[:nb_classes-1].sum() / (pixel_counter[:nb_classes-1].sum() + 1e-10)), f1
```

The **nan value** also appears in **mean_f1_score**, I calculate it by:

```
# the last class should be ignored
.mean_f1_score =f1_score[0:nb_classes-1].sum() / (nb_classes-1)
```

P.S. Why I don’t use the metrics function from sklearn is I think the transform from tensor to numpy(from GPU to CPU) is the time-wasting operation, and it will make GPU usage lower.

Correct me please if I am wrong.

Thanks in advance!