Creating subplots from multiple text files in a loop - matplotlib

Question

So I have been trying to load text files onto multiple subplots but the plots always seem to come up as one text file. Can anyone point me into the right #direction as to how to go about this?
import numpy as np
import matplotlib.pyplot as plt
RiverData1 = np.loadtxt('Gray1961.txt', skiprows = 2)
RiverData2 = np.loadtxt('Hack1957.txt', skiprows = 2)
RiverData3 = np.loadtxt('Rignon1996.txt', skiprows = 2)
RiverData4 = np.loadtxt('Robert1990.txt', skiprows = 2)
RiverData5 = np.loadtxt('Langbein1947_p145.txt', skiprows = 2)
RiverData6 = np.loadtxt('Langbein1947_p146.txt', skiprows = 2)
RiverData7 = np.loadtxt('Langbein1947_p149.txt', skiprows = 2)
RiverData8 = np.loadtxt('Langbein1947_p152.txt', skiprows = 2)
plotnums = 1
for plotnums in range (1,9):
plt.subplot(2,4,plotnums)
plt.plot((RiverData1[:,0]), (RiverData1[:,1]),'ko')
plt.plot((RiverData2[:,0]), (RiverData2[:,1]),'ko')
plt.plot((RiverData3[:,0]), (RiverData3[:,1]),'ko')
plt.plot((RiverData4[:,0]), (RiverData4[:,1]),'ko')
plt.plot((RiverData5[:,0]), (RiverData5[:,1]),'ko')
plt.plot((RiverData6[:,0]), (RiverData6[:,1]),'ko')
plt.plot((RiverData7[:,0]), (RiverData7[:,1]),'ko')
plt.plot((RiverData8[:,0]), (RiverData8[:,1]),'ko')
plt.xlabel('River Length (km)')
plt.ylabel('Area (Km$^2$)')
plt.xscale('log')
plt.yscale('log')
plotnums=plotnums+1
plt.show()

Answer 1

I suggest loading the data inside the loop as well. Additionally, you should capture the axis-handle in a variable to control which axis is used for plotting the data. To avoid any data artifacts, I suggest setting the variables to None at the end of each iteration.
import numpy as np
import matplotlib.pyplot as plt
# store your file names in a list to be able to iterate over them:
FILES = ['Gray1961.txt','Hack1957.txt','Rignon1996.txt',\
'Robert1990.txt','Langbein1947_p145.txt','Langbein1947_p146.txt',\
'Langbein1947_p149.txt','Langbein1947_p152.txt']
# specify desired conversion factors for each file, separated by x and y
xFactor =[1.00, 1.00, 1.00, 1.00\
2.59, 2.59, 2.59, 2.59]
yFactor = [1.000, 1.000, 1.000, 1.000\
1.609, 1.609, 1.609, 1.609]
# loop through all files;
# range(len(FILES)) returns a list of integers from 0 to 7 in this example
for n in range(len(FILES)):
# load the data from each file:
RiverData = np.loadtext(FILES[n], skiprows = 2)
# convert the data per the specified factors:
X = [xi * xFactor[n] for xi in RiverData[:,0]]
Y = [yi * yFactor[n] for yi in RiverData[:,1]]
# create sub-plot, here, you need to use n+1,
# because your loop iterable counts from 0,
# but your sub-plots count from 1
ax = plt.subplot(2,4,n+1)
# use the created axis object to plot your data;
# use ax.plot instead of plt.plot
ax.plot(X, Y,'ko')
# specify your axis details, again use ax.plot instead of plt.plot
ax.set_xlabel('River Length (km)')
ax.set_ylabel('Area (Km$^2$)')
# the file name can be used as plot title
# (if you want to omit the .txt ending, use [:-4]
# to omit the last for characters in the title string)
ax.set_title(FILES[n][:-4])
ax.set_xscale('log')
ax.set_yscale('log')
# to avoid surprises going from one loop to the next,
# clear the data from the variables
RiverData = None
ax = None
plt.show()
As Thiru pointed out you do not need to increment your iterable inside a for-loop.

Answer 2

Please check the matplotlib documentation on subplots
http://matplotlib.org/examples/animation/subplots.html
You can create a figure and add multiple subplots to it.
fig = plt.figure()
for plotnums in range(1,9):
plot1 = fig.add_subplot(2,4,plotnums) # update the numbers as required
...