Matplotlib giving no error but not plotting anything

Question

so this a section of my code, it runs and opens a graph but there is no plot points

fig =plt.figure(1)
data= [1.3,2.4]
for i in range(0,2):
    emittx=data[i];
    turns = 1+i;
    plt.plot(turns,emittx,'-r')
plt.show()

stuck because I cant really understand why

Can you give an example which is runnable? That is, containing data1? And I assume plt is matplotlib.pyplot? — Bach
– Bach, Commented Jan 29, 2014 at 10:48
why do you have plot(...) in a loop? I think you should be constructing lists/arrays of your x and y points and calling plot once. — three_pineapples
– three_pineapples, Commented Jan 29, 2014 at 10:54
Welcome to SO, sorry you got a rather unfriendly welcome. The problem is that you are plotting a single point using a line style with out markers. Change to plot(turns, emittx, 'or') and you will get markers. — tacaswell
– tacaswell, Commented Jan 29, 2014 at 14:34
Annoyingly all of the users who voted to close have no or minimal rep in python or matplotlib. There is enough information here for this to be a valid question. It would be better to include some fake-data to plot instead of trying to plot your actual data. — tacaswell
– tacaswell, Commented Jan 29, 2014 at 14:38
I figured the problem out, I took the plotting routine out of the loop (it wasnt supposed to be in there anyway) and wrote emittx and turns as an array and it plotted fine :) — mcrouch
– mcrouch, Commented Jan 29, 2014 at 15:16

Hamid · Accepted Answer · 2014-01-30 22:13:25Z

2

As was stated in the comments, the problem is because you are repeatedly (for loop) plotting a SINGLE point and asking matplotlib to use a line ('-') to connect the single point.

Either plot an array of two or more points (e.g. [2.3, 4.4]) or use markers to represent the data ('o'). For example:

fig =plt.figure(1)
data = [1.3,2.4]
for i in range(0,2):
    emittx=data[i];
    turns = 1+i;
    plt.plot(turns,emittx,'or', markersize=10)
plt.show()

should allow you to plot single points.

answered Jan 30, 2014 at 22:13

Hamid

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