import numpy as np

train_X_full = np.array([0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19])
print(train_X_full.size)

n = int((train_X_full.size)/2)
print(n)

train_X = np.array([])
train_X = np.random.choice(train_X_full, n, replace=False)
print(train_X.size)
print(train_X)