将一个数组中的值附加到另一个未知维度的数组

Question

I have an array A of dimension (654 X 2). Now within a loop, I have an 'if' statement. If for a value of 'i', the condition is true, I need to append the values of 'i'th row of A into a separate array B. That means the dimension of B is not known to me beforehand. So, how to initialize such array B in python. If this is not the procedure, suggest me alternative ways to execute the same.

Answer 1

You could initialize B as empty array:

B = []

Then when needs, just append it with the value:

B.append( [x,y] )

Answer 2

you do not provide ANY code to start from, please read this to learn how to ask a question How to create a Minimal, Complete, and Verifiable example

from the almost 0 information that you've provided

you should try doing something like this:

B = []
for i in range(n):
    if i % 2 == 0: # example of condition
        B += [ A[i] ]

print(B)