python - python27 matplotlib: first and last element connected

Question

Hi I have found the same problem but without an answer: enter link description here

My problem is that I try to plot data with the matplotlib and it connects the first and the last data point. I am using python27 and Windows 7. My problem is just to big to show complete so I just show some parts of the source code. The plot function is as below:

def plot(x, aw,temperature):
    plt.clf()
    temperatureplot = plt.subplot(211)
    awplot = plt.subplot(212)

    temperatureplot.grid()
    awplot.grid()  

    #set subplots
    awplot.set_ylabel('water activity aw')
    awplot.plot(x,aw)
    awplot.margins(y=0.05) #adds a gap between maximum value and edge of diagram
    temperatureplot.set_ylabel('Temperature in degree C')
    temperatureplot.plot(x,temperature)
    temperatureplot.margins(y=0.05)

    awplot.set_xlabel('Time in [hm]')
    plt.gcf().canvas.draw()

I am using this, because I am plotting this in a Tkinter Gui and want to refresh it sometimes. The plot looks like:

My values are:

t = [161000, 161015...., 191115]
aw = [0.618,......, 0.532]
temperature = [23.7,....,24.4]

Is it a problem that I do not start with zero in the t array?

If anybody has a hint or knows the problem please help me.

Cheers Max

Answer 1

Pyplot is connecting the first (x,y) point with the second (x,y) point, with the third and so on... so it looks like there may be a (duplicate?) low value hidden towards the end of your x.

You can try x == sorted(x) to double check if your list is strictly ascending. It will return False if it's not.

You will probably want to find the (x,y) pair before you call your plot() function, so I'll leave that to you for now.