Question

I am having a hard time creating a numpy 2D array on the fly.

So basically I have a for loop something like this.

for ele in huge_list_of_lists:
   instance = np.array(ele) 

creates a 1D numpy array of this list and now I want to append it to a numpy array so basically converting list of lists to array of arrays?

I have checked the manual.. and np.append() methods that doesn’t work as for np.append() to work, it needs two arguments to append it together.

Any clues?

Answer 1

Create the 2D array up front, and fill the rows while looping:

my_array = numpy.empty((len(huge_list_of_lists), row_length))
for i, x in enumerate(huge_list_of_lists):
    my_array[i] = create_row(x)

where create_row() returns a list or 1D NumPy array of length row_length.

Depending on what create_row() does, there might be even better approaches that avoid the Python loop altogether.