Data Visualization from a Data File
After you download the files above, complete this exercise.
Analyzing Data from Multiple Files
Overview 

Teaching: 20 min Exercises: 0 min 
Questions Objectives for loop to process multiple files. 
We now have almost everything we need to process all our data files. The only thing that's missing is a library with a rather unpleasant name:
import glob
The glob
library contains a function, also called glob
, that finds files and directories whose names match a pattern. We provide those patterns as strings: the character *
matches zero or more characters, while
?
matches any one character. We can use this to get the names of all the CSV files in the current directory:
print(glob.glob('inflammation*.csv'))
['inflammation05.csv', 'inflammation11.csv', 'inflammation12.csv', 'inflammation08.csv', 'inflammation03.csv', 'inflammation06.csv', 'inflammation09.csv', 'inflammation07.csv', 'inflammation10.csv', 'inflammation02.csv', 'inflammation04.csv', 'inflammation01.csv']
As these examples show, glob.glob
's result is a list of file and directory paths in arbitrary order. This means we can loop
over it to do something with each filename in turn. In our case, the "something" we want to do is generate a set of plots for each file in our inflammation dataset. If we want to start by analyzing just the first three files in alphabetical order,
we can use the sorted
builtin function to generate a new sorted list from the glob.glob
output:
import numpy import matplotlib.pyplot filenames = sorted(glob.glob('inflammation*.csv')) filenames = filenames[0:3] for f in filenames: print(f) data = numpy.loadtxt(fname=f, delimiter=',') fig = matplotlib.pyplot.figure(figsize=(10.0, 3.0)) axes1 = fig.add_subplot(1, 3, 1) axes2 = fig.add_subplot(1, 3, 2) axes3 = fig.add_subplot(1, 3, 3) axes1.set_ylabel('average') axes1.plot(numpy.mean(data, axis=0)) axes2.set_ylabel('max') axes2.plot(numpy.max(data, axis=0)) axes3.set_ylabel('min') axes3.plot(numpy.min(data, axis=0)) fig.tight_layout() matplotlib.pyplot.show()
inflammation01.csv
inflammation02.csv
inflammation03.csv
Sure enough, the maxima of the first two data sets show exactly the same ramp as the first, and their minima show the same staircase structure; a different situation has been revealed in the third dataset, where the maxima are a bit less regular, but the minima are consistently zero.
Plotting Differences 

Plot the difference between the average of the first dataset and the average of the second dataset, i.e., the difference between the leftmost plot of the first two figures.

Generate Composite Statistics 

filenames = glob.glob('inflammation*.csv') composite_data = numpy.zeros((60,40)) for f in filenames: # sum each new file's data into as it's read # # and then divide the composite_data by number of samples composite_data /= len(filenames) Then use pyplot to generate average, max, and min for all patients.

Key Points 
glob.glob(pattern) to create
a list of files whose names match a pattern.* in a pattern to match zero or more characters, and ? to match any single
character.

Source: Software Carpentry Foundation, http://swcarpentry.github.io/swcreleases/2017.08/pythonnoviceinflammation/04files/
This work is licensed under a Creative Commons Attribution 4.0 License.