Convert 2 python lists into 1 Numpy Array with the format ((list1, list2))

Question

Code:

import matplotlib.pyplot as plt
import numpy as np

poslist = []
numlist = []
i = 1

num = int(input('Number to check?'))
plt.title(str(num) + ': Collatz Graph')
plt.xlabel('Step')
plt.ylabel('Value')
print(num)
poslist.append(i)
numlist.append(num)

while True:
    i = i + 1
    if num % 2 == 0:
        num = num // 2
        print(num)
    elif num == 1:
        break
    else:
        num = num * 3
        num = num + 1
        print(num)
        poslist.append(i)
        numlist.append(num)

axislist = np.array((poslist, numlist))
print(axislist)
plt.plot(axislist)
plt.show()

I am trying to turn 2 lists into one Numpy Array. poslist, the first list, will add a number with each step that increments by 1 from the previous. (e.g [1, 2, 3, 4]). The second list, numlist, will append a number each step that corresponds with the Collatz Conjecture. I need to combine these two with the format: ((poslist, numlist)). This will then be input into the matplotlib.plot() function which will convert it to a graph. poslist will show the x-axis on the line graph, and numlist will show the y-axis. However, with the code I have, it does not output a continuous line of the value changing, but it outputs many coloured lines with no discernable origin, except that one starts at 0 and ends at the value that is run through the code on the y-axis, going from 0 to 1 on the x-axis:

Yeah that works, I just have to change it to plt.plot(*(poslist, numlist)). Thanks! — Commodore 64
– Commodore 64, Commented Nov 6, 2021 at 13:32
Well, plt.plot(*(poslist, numlist)) is just the same as plt.plot(poslist, numlist). Why do you want to complicate things so much? — JohanC
– JohanC, Commented Nov 6, 2021 at 13:35
honestly, I am very new to this so I wasn’t sure of the best solution. If there is a better way, I’ll use it. — Commodore 64
– Commodore 64, Commented Nov 6, 2021 at 14:01

EuxhenH · Accepted Answer · 2021-11-05 22:32:55Z

1

Do plt.plot(*axislist).

By default, plt.plot parses a single argument as y-coordinates. Hence, in your case each column is used to define a line. You need to pass both x coordinates and y coordinates, which you can do by adding *. In Python, * will split the numpy array into two subarrays defined by its rows.

answered Nov 5, 2021 at 22:32

EuxhenH

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