Gregor von Laszewski, laszewski@gmail.com

0. Introduction

This ipython script demonstrates how easy it is to interface java and python with ipython by using ipython as shell and postprocessing the data with matplotlib and/or pandas

The code to this ipython notebook can be found at

https://github.com/cloudmesh/cloudmesh/blob/master/ipython/

In particular this notebook is in

https://github.com/cloudmesh/cloudmesh/blob/master/ipython/Lesson%207%20-%20Interfaceing%20with%20Java.ipynb

The java code is in

https://github.com/cloudmesh/cloudmesh/tree/master/ipython/java

1. Setting Up The Environment

Several libraries may not yet be installed. Make sure you have jsonsche,ma and pandas



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pip install jsonschema



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pip install pandas

1.1 Lets look where we are



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!pwd









    



/Users/big/github/cloudmesh-new/cloudmesh/ipython

1.2 Just in case lest just clean the environment



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!cd java; rm -f data.csv *.class *~

1.3 Is Java available?



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!which java









    



/usr/bin/java

2. Program to interface with Java

2.1 Looking at the program

The program we use will just print a small number of values in csv format into a file so we can read it for plotting



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!ls java









    



data.java

Looking at the contenst of the file java/data.java



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!cat java/data.java









    



import java.io.*;

class data {
    public static void main(String args[]){
        try{	     
	    File r = new File("data.csv");
	    FileWriter pw = new FileWriter(r);
	    PrintWriter pr = new PrintWriter(pw);
	    pr.println("x,y");
	    pr.println("0.1,1");
	    pr.println("1.2,2");
	    pr.println("2.3,1.5");
	    pr.close();
	} catch(IOException e) {}
    }
}

Compiling the code



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!cd java; javac data.java

Looking at the output



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!ls java/*.class









    



java/data.class

3. Generating the Data



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!cd java; java data

Looking if the data is created



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!cat java/data.csv









    



x,y
0.1,1
1.2,2
2.3,1.5

4. Plotting

Enable inline plotting



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%pylab inline









    



Populating the interactive namespace from numpy and matplotlib

Importing the usual plotting libraries



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import numpy as np
import pandas as pd
import matplotlib.pyplot as plt

Reading the data from csv



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data = pd.read_csv('java/data.csv')



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print data









    



     x    y
0  0.1  1.0
1  1.2  2.0
2  2.3  1.5

Creating the Data frame



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df = pd.DataFrame(data, columns=['x', 'y'])



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df



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plt.scatter(df.x, df.y)









    Out[19]:





<matplotlib.collections.PathCollection at 0x10dac5ed0>



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