How can I print a Numpy Array as a result from a function?

Question

I have this function which gets 3 inputs and does some matrix calculations.

import numpy as np def func(input_x, output_y, lambda_param): if input_x.shape[0]<input_x.shape[1]: input_x = np.transpose(input_x) input_x = np.c_[np.ones(input_x.shape[0]),input_x] lambda_param = np.identity(input_x.shape[1])*lambda_param a = np.linalg.inv(lambda_param+np.matmul(np.transpose(input_x),input_x)) b = np.matmul(np.transpose(input_x),output_y) weights = np.matmul(a,b) weights = np.array([weights]) return weights

The function works well but I have a problem with the data type of the result. For example I have the inputs yy, xx and lamb:

 yy = np.array([208500, 181500, 223500, 140000, 250000, 143000, 307000, 200000, 129900, 118000]) xx = np.array([[1710, 1262, 1786, 1717, 2198, 1362, 1694, 2090, 1774, 1077], [2003, 1976, 2001, 1915, 2000, 1993, 2004, 1973, 1931, 1939]]) lamb = 10 result = func(xx, yy, lamb) print(result) #--> np.array([-576.67947107, 77.45913349, 31.50189177]) #print(result[2]) #--> 31.50189177

print(result) gives me [[-576.67947107 77.45913349 31.50189177]] but should return a numpy.array like np.array([-576.67947107, 77.45913349, 31.50189177])

and print(result[2]) should return 31.50189177 but gives an error because its not a np.array?

I hope you can help me! Thanks in advance.

Have you tried weights = np.array(weights) instead of weights = np.array([weights])? — Timus
– Timus, Commented Sep 30, 2020 at 22:35
I tried this but this would return [-576.67947107 77.45913349 31.50189177] 31.501891773638363 but not np.array([...]) — Triss
– Triss, Commented Sep 30, 2020 at 22:37
try checking the datatype of result using type(result). For me it is showing numpy.ndarray. — iadi7ya
– iadi7ya, Commented Sep 30, 2020 at 22:40
print(arr) shows the str format of the array, which omits the work array and commas. The repr gives more details. — hpaulj
– hpaulj, Commented Sep 30, 2020 at 23:29

jhihan · Accepted Answer · 2020-09-30 22:46:06Z

You don't need this line: weights = np.array([weights]) weights is already a 1D numpy array after weights = np.matmul(a,b). The redundant line will give an extra dimension to weights and the shape of weights becomes (1,3). You can check these by using print(weights.shape)

Jack Roberts · Accepted Answer · 2020-09-30 22:44:42Z

Removing the second to last line of func (weights = np.array([weights])) should fix it for you. You're unintentionally creating a two-dimensional array with that line. For example:

x = np.array([0.25, 0.50, 0.75]) print(x.shape) #--> (3,) print(x[2]) #--> 0.75 y = np.array([x]) print(y.shape) #--> (1, 3) print(y[2]) #--> IndexError

y above is a 2D array with length 1 in the first index and length 3 in the second index, so y[2] (which applies to the first index) doesn't exist.

You could do np.array(weights) instead (without putting weights in a list), but that's obsolete as weights is already a numpy array.

In terms of what's printed - you can check that weights really is a numpy array by doing print(type(weights)). It is a numpy array even if this isn't clear from print(weights).

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