CODEWITHSUNDEEP
pythonnumpyrandom
Mohamed Thasin ah
Mohamed Thasin ah

Reputation: 11192

Randomly pick index with constant interval

Is there any way randomly pick index of numpy array with constant interval.

For Example, I have an array with shape (1, 150) that is 5*30 elements. I want to randomly pick x indices where x<=30 for each 30 elements. So, totally I will have x*5 randomly picked indices from the array.

First, I tried with np.chocie but I can't use np.choice, because it doesn't look the constant interval.

I can go with loop iteration for each elements but I feel it's not the effective way.

Is there any way in numpy?

I tried this, it gives the required result. but I want to improve the code 

frames_picker = np.zeros(30*5)
samples=[]
for i in range(5):
    sample = (np.random.choice(frames_picker[0: 30].shape[0], 5, replace=False))+(i*30)
    samples.append(sample)
samples=np.array(samples)
frames_picker[np.sort(samples)]=1

Upvotes: 1

Views: 192

Answers (2)

kuzand
kuzand

Reputation: 9806

>>> np.random.choice(30, size=(5,5), replace=False) + np.arange(0, 150, 30)[:,None]

array([[ 18,  28,  13,   6,   8],
       [ 40,  56,  44,  57,  32],
       [ 83,  71,  65,  81,  64],
       [114, 115,  97,  90, 106],
       [137, 121, 129, 142, 149]])

You can then flatten and sort them. This gives you 5 random indices from each interval [0, 29], [30, 59], ..., [120, 149].

Upvotes: 2

Yann
Yann

Reputation: 2522

You can convert the 1D array to a more suitable 2D matrix and then apply sampling. For example:

data = np.array(...) # 1D array with 5*30 elements
m = np.asmatrix(np.split(data, 5))  # chunk and convert to a matrix
sample = m[np.random.randint(m.shape[0], size=30), :]  # get random 30 slices from the matrix
np.ravel(sample)  # convert back to 1D array

Upvotes: 0

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