plot in the same figure multiple lines from different data files with python

Question

I am new into the field of plotting in the same figure multiple lines from different data files with matplotlib in python. Currently I have the following script which is to plot column 1 and 2 from file 'statistics_paa_f0_vs_N.dat'. I want to be able also to plot in the same figure column 1 and 2 from file 'statistics_paa_f1_vs_N.dat'

#--- Import the necessary packages and modules
import matplotlib.pyplot as plt
import numpy as np

#--- initiate the list of coordinates for x and y lists
x,y = [],[]
#--- iterate over each line of the file and store it as a string
for line in open('statistics_paa_f0_vs_N.dat','r'):
    values = [float(s) for s in line.split()]
    x.append(values[0])
    y.append(values[1])

#--- plot the data
plt.plot(x,y,color='r',label='line1') # r - red colour
plt.xlabel('time (s)',fontsize=12)
plt.ylabel('Density (kg/m3)',fontsize=12)
plt.title('hi',fontsize=20,fontweight='bold')
plt.legend(loc='upper right')
plt.grid(False)
plt.axis(True)

#--- show and save the plot
plt.savefig('png_files-matplotlib/test.png')
plt.show()

pandas makes it really easy to read in files of different formats. Can also be used for plotting afterwards. — Mr. T
– Mr. T, Commented Nov 12, 2020 at 11:49

Mr. T · Accepted Answer · 2020-11-12 11:59:06Z

The simplest way to do this (without the usage of any external package) is to write a simple class that reads the file. Then, call class multiple times.

import matplotlib.pyplot as plt
import numpy as np


class ReadFile():

    def __init__(self,filename : str): 

        self.x = [] 
        self.y = []

        with open(filename,'r') as f:
            lines = f.readlines()
            for line in lines:
                val = [float(s) for s in line.split() ] 
                self.x.append(val[0])
                self.y.append(val[1])

        self.x = np.array(self.x,dtype=np.double)
        self.y = np.array(self.y,dtype=np.double)

    def getData(self):
        return self.x, self.y



file1 = ReadFile("./test")
file2 = ReadFile("./test1")

plt.plot(*file1.getData(), linewidth = 3.0, label = "test ")
plt.plot(*file2.getData(), linewidth = 3.0, label = "test1")


plt.xlabel('time (s)',fontsize=12)
plt.ylabel('Density (kg/m3)',fontsize=12)
plt.title('hi',fontsize=20,fontweight='bold')
plt.legend(loc='upper right')

   
plt.show()

Dimitris Mintis · Accepted Answer · 2020-11-11 20:02:57Z

although it is an unorthodox approach, one way of doing it is as such:

#--- Import the necessary packages and modules
import matplotlib.pyplot as plt
import numpy as np

#--- initiate the list of coordinates for x and y lists
x,y,z,e,l,m = [],[],[],[],[],[]
#--- iterate over each line of the file and store it as a string
for line in open('statistics_paa_f0_vs_N.dat','r'):
    values = [float(s) for s in line.split()]
    x.append(values[0])
    y.append(values[1])

for line in open('statistics_paa_f1_vs_N.dat','r'):
    values = [float(s) for s in line.split()]
    e.append(values[0])
    z.append(values[1])

for line in open('statistics_paa_f5_vs_N.dat','r'):
    values = [float(s) for s in line.split()]
    l.append(values[0])
    m.append(values[1])

#--- plot the data
plt.plot(x,y,'rs:',label='f=0')
plt.plot(e,z,'gs:',label='f=1')
plt.plot(l,m,'bs:',label='f=0.5')
#plt.plot(x,y,x,z,color='r',label='line1') # r - red colour
plt.xlabel('N (mer)',fontsize=12)
plt.ylabel('Density (kg/m3)',fontsize=12)
plt.title('hi',fontsize=20,fontweight='bold')
plt.legend(loc='upper right')
plt.grid(False)
plt.axis(True)

#--- show and save the plot
plt.savefig('png_files-matplotlib/test.png')
plt.show()

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