Compare a list and a tuple containing numpy arrays

Question

I have a python list which contains numpy arrays like:

a = [Numpy array 1, Numpy array 2, Numpy array 3]

These Numpy arrays are all 2D numpy arrays.

Now if i pick any two Numpy arrays from my list 'a' randomly and make a tuple, say,

b = (Numpy array 1, Numpy array 2)

How can i detect which arrays were picked i.e.

Numpy array 1, Numpy array 2

and which weren't i.e

Numpy array 3?

Let me repharse my question: Which numpy array from my list 'a' is not present in the tuple 'b'?

Why are you using a list? Do the arrays have different shape? — yatu
– yatu, Commented Mar 21, 2019 at 14:36
You could perhaps store the numpy arrays within a dict? That way you can assign a key to the array and maybe give away with the tuple? — Henry James
– Henry James, Commented Mar 21, 2019 at 14:47

Code Pope · Accepted Answer · 2019-03-21 18:00:17Z

1

You can do that by converting the numpy array to a list. Let's imagine this is your a and b:

import random
a = [np.arange(10).reshape(2,5), np.arange(10,20), np.arange(20,30)] # list of numpy arrays
first = random.randint(0,2)
second = first
while second==first:
    second = random.randint(0,2)
b = (a[first],a[second])

Now we want to know which element of a is not in the tuple b. You first convert the numpy arrays of b to list. Then you can check it with the elements of a which are also converted to list:

def arrayinList(arr, listOfArray):
    return next((True for elem in listOfArray if np.array_equal(elem, arr)), False)

missing_elem = [elem for elem in a if not arrayinList(elem,b) ]
print(missing_elem)

edited Mar 21, 2019 at 18:00

answered Mar 21, 2019 at 15:11

Code Pope

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5 Comments

Abdullah Ajmal Over a year ago

ValueError: The truth value of an array with more than one element is ambiguous. Use a.any() or a.all() this error is being thrown by this line: missing_elem = [elem for elem in i if list(elem) not in list_b]

Code Pope Over a year ago

@AbdullahAjmal what is i in your code? And have you defined list_b as the above code? The code I have written is tested dozen of times and runs without any error. I guess that you have not defined list_b as the above code. First copy the code in my answer and run it. It should run correctly. After that check what you have programmed differently.

Abdullah Ajmal Over a year ago

Your code is working fine. And i am editing your code exactly as above i.e Replacing your a and b accordingly to my a and b. But error still exists. I think the problem is 2D arrays? My numpy arrays are 2D arrays. While your arrays are 1D.

Code Pope Over a year ago

@AbdullahAjmal You are correct. I was assuming that your arrays are one dimensional. I have changed the code to also work for a list of arrays with different dimensions.

Abdullah Ajmal Over a year ago

yeah it works now. That's exactly what i wanted. thank you so much.

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