Python - turning text column into array, where I can access each number in the array

Question

I have a text file containing multiple columns. I can successfully print all the items in the 2 columns I am interested in by using this code:

with open(file) as catalog:
    for line in catalog:
        column = line.split()
        if not line.startswith('#'): #skipping column labels
            x = float(column[3])
            y = float(column[4])

Now if I add a print(x) command inside the 'if not' loop, it prints all of the x values. But if I put print(x) outside of the loop it only prints the last item. What I want is to be able to access the full array of x and y values anywhere in my code. I also need to be able to access the x/y array items individually, so I can say x[2], and it will give me the third value in the x array. I can not get this part to work even inside of the 'if not' loop. Thanks for any help, I have only been using Python for a couple of weeks..

Answer 1

Save your Xs and Ys in a list:

X_list = []
Y_list = []
with open(file) as catalog:
    for line in catalog:
        column = line.split()
        if not line.startswith('#'): #skipping column labels
            x = float(column[3])
            y = float(column[4])
            X_list.append(x)
            Y_list.append(y)
#then print the lists if you wish
print(X_list)
print(Y_list)

Answer 2

It sounds like you'll need to build a list of values.

with open(file) as catalog:
    x_values = []
    y_values = []
    for line in catalog:
        column = line.split()
        if not line.startswith('#'): #skipping column labels
            x_values.append(float(column[3]))
            y_values.append(float(column[4]))