Adjust legend labels for classes without instances (ultralytics#5174)

* legend-labels Adjust legend labels for classes without instances.

* ultralytics#5158 Re-indexed series names: only classes containing data.

* ultralytics#5158 Re-indexed series names: only classes containing data.

* Cleanup

Co-authored-by: Glenn Jocher <glenn.jocher@ultralytics.com>

utils/metrics.py

@@ -71,6 +71,8 @@ def ap_per_class(tp, conf, pred_cls, target_cls, plot=False, save_dir='.', names
 
     # Compute F1 (harmonic mean of precision and recall)
     f1 = 2 * p * r / (p + r + 1e-16)
+    names = [v for k, v in names.items() if k in unique_classes]  # list: only classes that have data
+    names = {i: v for i, v in enumerate(names)}  # to dict
     if plot:
         plot_pr_curve(px, py, ap, Path(save_dir) / 'PR_curve.png', names)
         plot_mc_curve(px, f1, Path(save_dir) / 'F1_curve.png', names, ylabel='F1')