How do I plot y=x+i for i = [1:16]?

Question

I should be getting 16 individual lines, but the endpoint of the first line back tracks and meets the starting point of the next line. How do I fix this?

a = []
b = []
x = 0
for i in range(1,17):
    for x in range(0,5):
        y=x+i
        a.append(x)
        b.append(y)

fig= plt.figure()
axes=fig.add_subplot(111)
pylab.plot(a, b, '-b')

Answer 1

The problem is that you are trying to plot 16 lines but appending them all to a single list. The solution is to initialize empty lists each time and them plot them inside the for loop so that each list gets plotted as a single line.

You should define the figure only once outside the for loop in this case.

In the below answer, I am removing things which you don't need. For ex. x=0 and axes=fig.add_subplot(111) . I am replacing this command by another variant.

---

---

Complete working answer:

import matplotib.pyplot as plt

fig, ax = plt.subplots(figsize=(8,6))

for i in range(1,17):
    a = []
    b = []
    for x in range(0,5):
        y=x+i
        a.append(x)
        b.append(y)
    plt.plot(a, b, '-b')
plt.show()       

Simpler version

You can simplify your whole code by making using of a numpy array as

import numpy as np
import matplotib.pyplot as plt

fig, ax = plt.subplots(figsize=(8,6))

a = np.arange(5)

for i in range(1,17):
    plt.plot(a, a+i, '-b')

plt.show()

Answer 2

As your x values are always the same, you can pass them as a 1D array and your y values as a 2D array. matplotlib will then automatically take care of the colouring:

x = np.linspace(0,5,10)
y0 = i0 = np.arange(17)
y = y0[:,None]+x
plt.plot(x,y.T)
plt.show()

gives this image:

Answer 3

As you are appending all the answers in a single list, it assumes all lines are connected. You can try fixing sizes of a and b to 5 and then plot each of the 16 lines after each pass of the inner for loop.

for i in range(1,17):
    for x in range(0,5):
        y=x+i
        a.append(x)
        b.append(y)
        pylab.plot(a, b, '-b')
    a=[]
    b=[]

fig= plt.figure()
axes=fig.add_subplot(111)

pylab.show()