Add Hub results.pandas() method (#2725)

* Add Hub results.pandas() method

New method converts results from torch tensors to pandas DataFrames with column names.

This PR may partially resolve issue https://github.com/ultralytics/yolov5/issues/2703

```python
results = model(imgs)

print(results.pandas().xyxy[0])
         xmin        ymin        xmax        ymax  confidence  class    name
0   57.068970  391.770599  241.383545  905.797852    0.868964      0  person
1  667.661255  399.303589  810.000000  881.396667    0.851888      0  person
2  222.878387  414.774231  343.804474  857.825073    0.838376      0  person
3    4.205386  234.447678  803.739136  750.023376    0.658006      5     bus
4    0.000000  550.596008   76.681190  878.669922    0.450596      0  person
```

* Update comments 

torch example input now shown resized to size=640 and also now a multiple of P6 stride 64 (see https://github.com/ultralytics/yolov5/issues/2722#issuecomment-814785930)

* apply decorators

* PEP8

* Update common.py

* pd.options.display.max_columns = 10

* Update common.py

models/common.py

@@ -1,14 +1,15 @@
 # YOLOv5 common modules
 
 import math
+from copy import copy
 from pathlib import Path
 
 import numpy as np
+import pandas as pd
 import requests
 import torch
 import torch.nn as nn
 from PIL import Image
-from torch.cuda import amp
 
 from utils.datasets import letterbox
 from utils.general import non_max_suppression, make_divisible, scale_coords, increment_path, xyxy2xywh
@@ -235,14 +236,16 @@ class autoShape(nn.Module):
         print('autoShape already enabled, skipping... ')  # model already converted to model.autoshape()
         return self
 
+    @torch.no_grad()
+    @torch.cuda.amp.autocast()
     def forward(self, imgs, size=640, augment=False, profile=False):
-        # Inference from various sources. For height=720, width=1280, RGB images example inputs are:
+        # Inference from various sources. For height=640, width=1280, RGB images example inputs are:
         #   filename:   imgs = 'data/samples/zidane.jpg'
         #   URI:             = 'https://github.com/ultralytics/yolov5/releases/download/v1.0/zidane.jpg'
-        #   OpenCV:          = cv2.imread('image.jpg')[:,:,::-1]  # HWC BGR to RGB x(720,1280,3)
+        #   OpenCV:          = cv2.imread('image.jpg')[:,:,::-1]  # HWC BGR to RGB x(640,1280,3)
-        #   PIL:             = Image.open('image.jpg')  # HWC x(720,1280,3)
+        #   PIL:             = Image.open('image.jpg')  # HWC x(640,1280,3)
-        #   numpy:           = np.zeros((720,1280,3))  # HWC
+        #   numpy:           = np.zeros((640,1280,3))  # HWC
-        #   torch:           = torch.zeros(16,3,720,1280)  # BCHW
+        #   torch:           = torch.zeros(16,3,320,640)  # BCHW (scaled to size=640, 0-1 values)
         #   multiple:        = [Image.open('image1.jpg'), Image.open('image2.jpg'), ...]  # list of images
 
         t = [time_synchronized()]
@@ -275,7 +278,6 @@ class autoShape(nn.Module):
         x = torch.from_numpy(x).to(p.device).type_as(p) / 255.  # uint8 to fp16/32
         t.append(time_synchronized())
 
-        with torch.no_grad(), amp.autocast(enabled=p.device.type != 'cpu'):
         # Inference
         y = self.model(x, augment, profile)[0]  # forward
         t.append(time_synchronized())
@@ -347,17 +349,27 @@ class Detections:
         self.display(render=True)  # render results
         return self.imgs
 
-    def __len__(self):
+    def pandas(self):
-        return self.n
+        # return detections as pandas DataFrames, i.e. print(results.pandas().xyxy[0])
+        new = copy(self)  # return copy
+        ca = 'xmin', 'ymin', 'xmax', 'ymax', 'confidence', 'class', 'name'  # xyxy columns
+        cb = 'xcenter', 'ycenter', 'width', 'height', 'confidence', 'class', 'name'  # xywh columns
+        for k, c in zip(['xyxy', 'xyxyn', 'xywh', 'xywhn'], [ca, ca, cb, cb]):
+            a = [[x[:5] + [int(x[5]), self.names[int(x[5])]] for x in x.tolist()] for x in getattr(self, k)]  # update
+            setattr(new, k, [pd.DataFrame(x, columns=c) for x in a])
+        return new
 
     def tolist(self):
         # return a list of Detections objects, i.e. 'for result in results.tolist():'
-        x = [Detections([self.imgs[i]], [self.pred[i]], self.names) for i in range(self.n)]
+        x = [Detections([self.imgs[i]], [self.pred[i]], self.names, self.s) for i in range(self.n)]
         for d in x:
             for k in ['imgs', 'pred', 'xyxy', 'xyxyn', 'xywh', 'xywhn']:
                 setattr(d, k, getattr(d, k)[0])  # pop out of list
         return x
 
+    def __len__(self):
+        return self.n
+
 
 class Classify(nn.Module):
     # Classification head, i.e. x(b,c1,20,20) to x(b,c2)

utils/general.py

@@ -13,6 +13,7 @@ from pathlib import Path
 
 import cv2
 import numpy as np
+import pandas as pd
 import torch
 import torchvision
 import yaml
@@ -24,6 +25,7 @@ from utils.torch_utils import init_torch_seeds
 # Settings
 torch.set_printoptions(linewidth=320, precision=5, profile='long')
 np.set_printoptions(linewidth=320, formatter={'float_kind': '{:11.5g}'.format})  # format short g, %precision=5
+pd.options.display.max_columns = 10
 cv2.setNumThreads(0)  # prevent OpenCV from multithreading (incompatible with PyTorch DataLoader)
 os.environ['NUMEXPR_MAX_THREADS'] = str(min(os.cpu_count(), 8))  # NumExpr max threads