how do I extract the elements with the same value in a list-CodePudding

I have a group of data in the format of:

log = [[timestamp, x_coordinate, y_coordinate]]

which looks something like:

log = [[500, 20, 20], [500, 25, 25], [500, 22, 25], [1000, 20, 25], [1000, 30, 25]...]

There is quite a lot of data so I want to process them faster. Is there a way to process the data with the same timestamp altogether and then move on to the next timestamp?

So far I have tried to use for loop to do the favor, but it still works very slow. Is there another way to process the data faster?

for item in log:
     if item[0] == ts:
          draw_tracking(output_img, item[1], item[2])

Desired output is a bit complicated. I want to draw a box based on the data from the list. I have this function:

def draw_tracking(img, x, y):
    pt_1 = (x, y)
    pt_2 = ((x 5), (y 5))
    cv2.rectangle(img, pt1=pt_1, pt2=pt_2, color=(255,0,0), thickness=5)
    plt.imshow(img)

CodePudding user response：

You can do a pre process first, something like this:

from collections import defaultdict

grouped = defaultdict(list)

for item in log:
    grouped[item[0]] = (item[1], item[2])

Now, when you want to draw a timestamp (ts), you can do:

for item in grouped[ts]:
    draw_tracking(output_img, item[0], item[1])

This way you only iterate over the full list onece, for the preprocess, then, for each timestamp, you only iterate over that timestamp "entries".

CodePudding user response：

if you wanna to find out the data of a given timestamp, the fllowing code may works:

[{'timestamp': _[0], 'data': _} for _ in log if _[0] == YOUR_TIMESTAMP ]

if you wanna to group the data by timestamp, you may consider the code bellow

{_[0]: [__ for __ in log if __[0]==_[0]]  for _ in log}