josh1234 josh1234 - 1 month ago 20
Python Question

Using Numpy Array to Create Unique Array

Can you create a numpy array with all unique values in it?

myArray = numpy.random.random_integers(0,100,2500)
myArray.shape = (50,50)


So here I have a given random 50x50 numpy array, but I could have non-unique values. Is there a way to ensure every value is unique?

Thank you

Update:



I have created a basic function to generate a list and populate a unique integer.

dist_x = math.sqrt(math.pow((extent.XMax - extent.XMin), 2))
dist_y = math.sqrt(math.pow((extent.YMax - extent.YMin),2))
col_x = int(dist_x / 100)
col_y = int(dist_y / 100)
if col_x % 100 > 0:
col_x += 1
if col_y % 100 > 0:
col_y += 1
print col_x, col_y, 249*169
count = 1
a = []

for y in xrange(1, col_y + 1):
row = []
for x in xrange(1, col_x + 1):
row.append(count)
count += 1
a.append(row)
del row

numpyArray = numpy.array(a)


Is there a better way to do this?

Thanks

Answer

The most convenient way to get a unique random sample from a set is probably np.random.choice with replace=False.

For example:

import numpy as np

# create a (5, 5) array containing unique integers drawn from [0, 100]
uarray = np.random.choice(np.arange(0, 101), replace=False, size=(5, 5))

# check that each item occurs only once
print((np.bincount(uarray.ravel()) == 1).all())
# True

If replace=False the set you're sampling from must, of course, be at least as big as the number of samples you're trying to draw:

np.random.choice(np.arange(0, 101), replace=False, size=(50, 50))
# ValueError: Cannot take a larger sample than population when 'replace=False'

If all you're looking for is a random permutation of the integers between 1 and the number of elements in your array, you could also use np.random.permutation like this:

nrow, ncol = 5, 5
uarray = (np.random.permutation(nrow * ncol) + 1).reshape(nrow, ncol)