CODEWITHSUNDEEP
pythonnumpylambdamultidimensional-array
user2758991
user2758991

Reputation: 7

Passing multiple columns of a 2D array into a lambda function and returning a single column array

I am missing something simple here. I cannot figure out how to pass multiple columns of a 2D array (matrix) and output them as a single column array.

Here is a simple example:

import numpy as np

Z = lambda x1,x2: (x1*x2 - 3)^2 + 1

# a sample 2D array with 15 rows and 2 columns    
x= np.arange(30).reshape((15,2))

answer = [Z(i[0],i[1]) for i in x]

The last line of code is where my problem lies. I would like the output to be a single column array with 15 rows.

As a final note: My code only uses 2 columns as inputs. If it could be further expanded to a flexible number of columns, it would be greatly appreciated.

Upvotes: 0

Views: 3912

Answers (2)

Magellan88
Magellan88

Reputation: 2573

You could do

import numpy as np

Z = lambda data, i, j: ((data[:,i]*data[:,j] - 3)**2 + 1)[:,np.newaxis]

# a sample 2D array with 15 rows and 2 columns    
x= np.arange(30).reshape((15,2))

answer = Z(x,0,1)

so maybe you don't need the lambda function after all

Upvotes: 1

Lee
Lee

Reputation: 31050

Could you make your last line:

answer = np.array([Z(i[0],i[1]) for i in x]).reshape(15,1)

which gives:

array([[ -2],
       [  0],
       [ 18],
       [ 36],
       [ 70],
       [104],
       [154],
       [204],
       [270],
       [336],
       [418],
       [500],
       [598],
       [696],
       [810]])

Upvotes: 1

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