plotting multiple plots generated inside a for loop on the same axess

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
– MaxNoe, Commented Oct 14, 2014 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
– Michael Hlabathe, Commented Oct 15, 2014 at 9:08

Ffisegydd · Accepted Answer · 2014-10-14 08:50:38Z

28

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, 2014 at 8:50

Ffisegydd

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2 Comments

Michael Hlabathe Over a year ago

Thanks, noted.Is there a way of avoiding for loops?

Ffisegydd Over a year ago

@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.

MaxNoe · Accepted Answer · 2014-10-14 16:08:27Z

4

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()

answered Oct 14, 2014 at 16:08

MaxNoe

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1 Comment

Michael Hlabathe Over a year ago

It's the first time i come across genfromtxt, it is handy and thanks for the update

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