How to create a numpy list from within a loop

Question

I have a numpy list of arrays (a two-dimensional list):

db = [ch1, ch2, ch3, ch4, ch5, ch6, ch7, ch8, ch9, ch10, ch11, ch12, ch13, ch14, ch15, ch16]

I would like to perform some operations in these arrays like this:

for i in db:
 newch = (eegFilter(i)/sens)+25

How can I create a new two-dimensional list with the results of each loop iteration so that the new array would look something like this:

[[newch_iteration_1], [newch_iteration_2], [newch_iteration_3], ....]

• user2357112: Lists and arrays are very different things. A list of arrays is not a two-dimensional list, and neither a list of arrays nor a 2D list is what you should be using, which is a 2D array. If you're using NumPy, you want to avoid using lists to hold or work with numbers. What are you actually using to store your data?
• Carlos Muñiz: thank you for the clarification. the python script reads the data from a csv file and then stores it in a 2D list to manipulate it. is this not the most efficient way. the data files are usually very big (hundreds of megs)

Answer 1

Use a list comprehension:

[((eegFilter(i)/sens)+25).reshape(1, *i.shape) for i in db]

Demo:

In [12]: db = [np.arange(10).reshape(2, 5), np.arange(12).reshape(3, 4)]
In [13]: [(x%2).reshape(1, *x.shape) for x in db] 
Out[13]: 
[array([[[0, 1, 0, 1, 0], 
 [1, 0, 1, 0, 1]]]), 
 array([[[0, 1, 0, 1], 
 [0, 1, 0, 1], 
 [0, 1, 0, 1]]])]