What I'm trying to do is to put each index 0 of each item of list a in the list x and each index 1 of each item of list a in the list y. When the plot is shown, it only appears one point. Does anybody know what am I doing wrong? Thanks in advance.
a = [[1,2], [2,3], [3,4], [5,6], [6,7]]
for item in a:
x = [ ]
y = [ ]
x.append(item[0])
y.append(item[1])
plt.plot(x, y, 'ro')
plt.axis([-50, 50, -50, 50])
plt.show()
You overwrite the values of x and y every time through the loop, so only the last point is stored. Move your declaration of x and y outside of your loop.
It makes more sense to take advantage of Python's list comprehensions though:
x, y = ([p for p,q in a], [q for p,q in a])
plt.plot(x, y, 'ro')
plt.axis([-50, 50, -50, 50])
plt.show()
List comprehension:
([p for p,q in a], [q for p,q in a])
this piece of code returns a 2-tuple whose elements are two Python lists. The lists are formed using a list comphrehension which takes each list of x,y and splits the xs into the first returned list, and the ys into the second.
Try this:
x, y = zip(*a)
It is compact and readable and it should work.
