How do I turn x1, x2, y1, y2 array into rectangular vertices array?-CodePudding

Say I have a two dimensional array of 4 columns, let's name the columns x1, x2, y1, y2, the data of the array are floats between 0 and 1, x2 is always larger than x1 and y2 is always larger than y1.

Each row represents a rectangle whose lower left corner is at (x1, y1) and whose width is x2-x1 and whose height is y2-y1.

The array is created like this:


import numpy as np

bounds = np.random.uniform(size=(100, 4))
bounds[:,:2].sort(1)
bounds[:,2:].sort(1)

Now how do I create rectangular vertices from the array in this order: lower left, lower right, upper right, upper left, without using for loops?

I can do this:


rectangles = [[(x1, y1), (x2, y1), (x2, y2), (x1, y2)] for x1, x2, y1, y2 in bounds]

But that defeats the purpose of using arrays in the first place.

Instead I can do these:

lower_left = np.array((bounds[:, 0], bounds[:, 2])).T
lower_right = np.array((bounds[:, 1], bounds[:, 2])).T
upper_right = np.array((bounds[:, 1], bounds[:, 3])).T
upper_left = np.array((bounds[:, 0], bounds[:, 3])).T

Now I only need to figure out how to join the columns horizontally so that each row in the columns stays a sub row.

I have tried to do this:

np.hstack((lower_left, lower_right, upper_right, upper_left))

But it isn't exactly working as intended, the fields are joined, I need the points to stay separate for reasons that are irrelevant to the question.

How can I achieve exactly the same result as my list comprehension using vectorization?

Edit

I just figured out how to unpack array to columns:

lower_left, lower_right, upper_right, upper_left = bounds.T

Keep in mind I wrote all of these on an Android phone and I don't have physical access to actual computer on which I can do programming during nighttime (it is nighttime at my locale at time of writing), it is a complicated matter I won't discuss here.

The thing is I can't run complex code, for simple code using only built-in functions or standard library I can use w3c school's Python TryIt editor to run the code, but for anything requiring imports of any library installed via pip, I can't run the code, so I can't know for sure if my example will run.

Edit

Fixed bug in example code, I wrote all of these on a phone so I can't run the code.

CodePudding user response：

I have already done it, I will post the code below just so that it may help anyone who stumbles here by Google searching:

import numpy as np

values = np.random.random((100, 4))
values[:, :2].sort(1)
values[:, 2:].sort(1)
x1, x2, y1, y2 = values.T
ll = np.array((x1, y1)).T
lr = np.array((x2, y1)).T
ur = np.array((x2, y2)).T
ul = np.array((x1, y2)).T
rects = np.stack((ll, lr, ur, ul), axis=1)
rects.shape

It produces this:

(100, 4, 2)

Sample:

array([[[0.0296138 , 0.29131621],
        [0.3693961 , 0.29131621],
        [0.3693961 , 0.97544314],
        [0.0296138 , 0.97544314]],

       [[0.51630027, 0.39519657],
        [0.59897507, 0.39519657],
        [0.59897507, 0.76210139],
        [0.51630027, 0.76210139]],

       [[0.84594749, 0.42784315],
        [0.86691432, 0.42784315],
        [0.86691432, 0.79314211],
        [0.84594749, 0.79314211]],

       [[0.34412745, 0.21132195],
        [0.68466905, 0.21132195],
        [0.68466905, 0.25444418],
        [0.34412745, 0.25444418]],

       [[0.08766792, 0.39237762],
        [0.89154757, 0.39237762],
        [0.89154757, 0.44256892],
        [0.08766792, 0.44256892]],

       [[0.05022344, 0.54610173],
        [0.73931811, 0.54610173],
        [0.73931811, 0.96692603],
        [0.05022344, 0.96692603]],

       [[0.51423357, 0.48105812],
        [0.90815268, 0.48105812],
        [0.90815268, 0.93234461],
        [0.51423357, 0.93234461]],

       [[0.18887874, 0.28019687],
        [0.59905412, 0.28019687],
        [0.59905412, 0.61594758],
        [0.18887874, 0.61594758]],

       [[0.00589912, 0.50042431],
        [0.02952724, 0.50042431],
        [0.02952724, 0.93056696],
        [0.00589912, 0.93056696]],

       [[0.2267573 , 0.04920763],
        [0.43967406, 0.04920763],
        [0.43967406, 0.92892994],
        [0.2267573 , 0.92892994]],

       [[0.2885361 , 0.70178778],
        [0.73626986, 0.70178778],
        [0.73626986, 0.71951917],
        [0.2885361 , 0.71951917]],

       [[0.50806757, 0.2228232 ],
        [0.64801743, 0.2228232 ],
        [0.64801743, 0.58853764],
        [0.50806757, 0.58853764]],

       [[0.52227217, 0.08670711],
        [0.79866514, 0.08670711],
        [0.79866514, 0.95127646],
        [0.52227217, 0.95127646]],

       [[0.09714329, 0.38051135],
        [0.68042731, 0.38051135],
        [0.68042731, 0.6425565 ],
        [0.09714329, 0.6425565 ]],

       [[0.28889578, 0.83151436],
        [0.58681713, 0.83151436],
        [0.58681713, 0.94071716],
        [0.28889578, 0.94071716]],

       [[0.2109561 , 0.05147464],
        [0.52700784, 0.05147464],
        [0.52700784, 0.21706122],
        [0.2109561 , 0.21706122]]])

CodePudding user response：

With fancy indexes, you can avoid unnecessary stacked arrays:

>>> rand = np.random.rand(10, 4)
>>> rand
array([[0.9975164 , 0.24502806, 0.39619553, 0.07442783],
       [0.57017416, 0.08316826, 0.16822264, 0.93233668],
       [0.62260765, 0.77285638, 0.30093986, 0.76024642],
       [0.26245902, 0.42329171, 0.31591031, 0.1685193 ],
       [0.55910866, 0.33132002, 0.37912662, 0.99307642],
       [0.02038662, 0.11176963, 0.72928163, 0.6766679 ],
       [0.59143993, 0.03891871, 0.80613796, 0.34442057],
       [0.47100568, 0.98703327, 0.60235766, 0.97791171],
       [0.63499569, 0.94171562, 0.06308767, 0.78651194],
       [0.679388  , 0.0464196 , 0.37712365, 0.76514397]])
>>> rand[:, :2].sort(1)
>>> rand[:, 2:].sort(1)
>>> rand[:, [0, 2, 1, 2, 1, 3, 0, 3]].reshape(-1, 4, 2)
array([[[0.24502806, 0.07442783],
        [0.9975164 , 0.07442783],
        [0.9975164 , 0.39619553],
        [0.24502806, 0.39619553]],

       [[0.08316826, 0.16822264],
        [0.57017416, 0.16822264],
        [0.57017416, 0.93233668],
        [0.08316826, 0.93233668]],

       [[0.62260765, 0.30093986],
        [0.77285638, 0.30093986],
        [0.77285638, 0.76024642],
        [0.62260765, 0.76024642]],

       [[0.26245902, 0.1685193 ],
        [0.42329171, 0.1685193 ],
        [0.42329171, 0.31591031],
        [0.26245902, 0.31591031]],

       [[0.33132002, 0.37912662],
        [0.55910866, 0.37912662],
        [0.55910866, 0.99307642],
        [0.33132002, 0.99307642]],

       [[0.02038662, 0.6766679 ],
        [0.11176963, 0.6766679 ],
        [0.11176963, 0.72928163],
        [0.02038662, 0.72928163]],

       [[0.03891871, 0.34442057],
        [0.59143993, 0.34442057],
        [0.59143993, 0.80613796],
        [0.03891871, 0.80613796]],

       [[0.47100568, 0.60235766],
        [0.98703327, 0.60235766],
        [0.98703327, 0.97791171],
        [0.47100568, 0.97791171]],

       [[0.63499569, 0.06308767],
        [0.94171562, 0.06308767],
        [0.94171562, 0.78651194],
        [0.63499569, 0.78651194]],

       [[0.0464196 , 0.37712365],
        [0.679388  , 0.37712365],
        [0.679388  , 0.76514397],
        [0.0464196 , 0.76514397]]])