plotting multiple plots generated inside a for loop on the same axes python

Question

My code is as follows, the problem is instead of having one plot, I get 242 plots. I tried putting the plt.show() outside the loop, it didn't work.

import numpy as np
import matplotlib.pyplot as plt
import csv

names = list()

with open('selected.csv','rb') as infile:
    reader = csv.reader(infile, delimiter = ' ')
    for row in reader:
        names.append(row[0])

names.pop(0)

for j in range(len(names)):
    filename = '/home/mh/Masters_Project/Sigma/%s.dat' %(names[j])
    average, sigma = np.loadtxt(filename, usecols = (0,1), unpack = True, delimiter = ' ')
    name = '%s' %(names[j]) 
    plt.figure()
    plt.xlabel('Magnitude(average)', fontsize = 16)
    plt.ylabel('$\sigma$', fontsize = 16)
    plt.plot(average, sigma, marker = '+', linestyle = '', label = name)
plt.legend(loc = 'best')
plt.show()

you should not use `for i in range(len(xs))` and `xs[i]` to iterate over elements of an array. Use `for x in xs:`. Another Point: Why do you use such a complicated way for reading in the names? `names = np.genfromtxt("selected.csv", delimiter=" ", dtype=np.str, skiprows=1)` — MaxNoe, Oct 14 '14 at 16:00
Thanks very much. Usually I don't work with csv files, but your way is a short and neat way of doing. — Michael Hlabathe, Oct 15 '14 at 09:08

score 27 · Answer 1 · answered Oct 14 '14 at 08:50

27

Your issue is that you're creating a new figure with every iteration using plt.figure(). Remove this line from your for loop and it should work fine, as this short example below shows.

import matplotlib.pyplot as plt
import numpy as np

x = np.arange(10)

for a in [1.0, 2.0, 3.0]:
    plt.plot(x, a*x)

plt.show()

Example plot

answered Oct 14 '14 at 08:50

Ffisegydd

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Thanks, noted.Is there a way of avoiding for loops? – Michael Hlabathe Oct 15 '14 at 09:12
@MichaelHlabathe that is a different question entirely to the one you've asked. I would suggest you ask a new question in this case, rather than me editing my answer to answer something different. – Ffisegydd Oct 15 '14 at 09:15

score 4 · Answer 2 · answered Oct 14 '14 at 16:08

Let me improve your code a bit:

import numpy as np
import matplotlib.pyplot as plt

# set the font size globally to get the ticklabels big too:
plt.rcParams["font.size"] = 16

# use numpy to read in the names
names = np.genfromtxt("selected.csv", delimiter=" ", dtype=np.str, skiprows=1)

# not necessary butyou might want to add options to the figure
plt.figure()

# don't use a for i in range loop to loop over array elements
for name in names:
    # use the format function
    filename = '/home/mh/Masters_Project/Sigma/{}.dat'.format(name)

    # use genfromtxt because of better error handling (missing numbers, etc)
    average, sigma = np.genfromtxt(filename, usecols = (0,1), unpack = True, delimiter = ' ')

    plt.xlabel('Magnitude(average)')
    plt.ylabel('$\sigma$')
    plt.plot(average, sigma, marker = '+', linestyle = '', label = name)

plt.legend(loc = 'best')
plt.show()

It's the first time i come across genfromtxt, it is handy and thanks for the update — Michael Hlabathe, Oct 15 '14 at 09:10

plotting multiple plots generated inside a for loop on the same axes python

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