Saturday, December 1, 2012

Matlab, Octove or Python for Machine Learning

but  my adviser uses Matlab

I start implementing ML algorithms after learning theory behind them however I really got stuck in which tool to write my code. There are 3 options for now: Octave, Matlab and Python  (read discussions). You can check my previous posts about python, I switched to Python after learning Perl. For now, it seems that for implementation of machine learning algorithms preferring Matlab is a good decision.

There are other tools such as R, Sage etc. i really don't know which one to master, but for now my adviser uses matlab exclusively, so do i.

I list some useful posts that are good when you make your decision :





Friday, September 14, 2012

Switching From Perl to Python, Step 5 First Step into Machine Learning

in this post i share my experience while searching about the python machine learning modules. There are lots of them, i think that there is no one that can be used for all algorithms, so for a specific algorithm you can choose one of them that satisfies your need.

First i start reading  Scientific Scripting with Python for Computational Immunology, this is the best, short tutorial ever to understand the basic statistics. While going through stackoverflow questions, i realized that many people recommend scikit-learn: machine learning in Python.

i'm familiar with matplotlib and pyplot, however now in examples another module pylab is imported. Clarification: matplotlib, pyplot, and pylab from (http://truongnghiem.wordpress.com):

pyplot is just a wrapper module to provide a Matlab-style interface to matplotlib.
Many plotting functions in Matlab are provided by pyplot with the same names and arguments.
This will ease the process of moving from Matlab to Python for scientific computation.
pylab is basically a mode in which pyplot and numpy are imported in a single namespace,
thus making the Python working environment very similar to Matlab. By importing pylab: 
from pylab import *
we can use Matlab-style commands like:
x = arange(0, 10, 0.2)
y = sin(x)
plot(x, y)

Ok. Let's start, first i try simple linear regression from Scientific Scripting with Python for Computational Immunology. We have dilution.cvs file that contains the data of:
Dilution Factor,Rep 1,Rep 2,Rep 3,Mean,sd
1,15.16,14.95,14.55,14.89,0.31
2,15.36,15.61,15.51,15.49,0.13
4,16.65,16.88,16.71,16.75,0.12
8,18.07,17.60,18.13,17.93,0.29
16,18.86,19.63,19.39,19.29,0.39
32,20.39,19.40,20.39,20.06,0.57
64,21.44,20.76,21.22,21.14,0.35
128,21.90,22.04,21.94,21.96,0.07
256,22.87,22.77,23.36,23.00,0.32
512,23.98,23.92,24.24,24.05,0.17
1024,24.91,24.83,24.92,24.89,0.05
2048,26.37,25.43,26.21,26.00,0.50
Dilution and Factor columns are used in order to implement the linear regression in two dimensional space where the line is defined as :

'''
 *@author beck 
 *@date Sep 14, 2012
 *Basic Statistics with Python 
 *bekoc.blogspot.com 
'''

import numpy
import matplotlib.pyplot as plt
#import pylab, # from pylab import *
import scipy.stats as stats

xs= numpy.loadtxt("dilution.csv",delimiter=",", skiprows=1, usecols=(0,1)) 
# numpy array - similar to C array notation.
x= numpy.log2(xs[:,0])
y=xs[:,1]

plt.plot(x,y,"x")
        
plt.xlabel('Number of Dilutions(log2)')
plt.ylabel('Rep1')
plt.title('Linear Regression example')
plt.legend()

slope, intercept, r_value, p_value, std_error = stats.linregress(x,y)
plt.plot(x,intercept+slope*x,"r-") # y=mx+b where m is slope and b is intercept
#plt.plot(x,x**2)
plt.show()

straight line seems reasonable

Resources for machine learning:

Tuesday, September 4, 2012

Switching From Perl to Python, Step 4 Basic Statistics


On August 28 2012 at 10am, the creator of matplotlib, John D. Hunter died from complications arising from cancer treatment, after a brief but intense battle with this terrible illness. John is survived by his wife Miriam, his three daughters Rahel, Ava and Clara, his sisters Layne and Mary, and his mother Sarah.
If you have benefited from John's many contributions, please say thanks in the way that would matter most to him. Please consider making a donation to the John Hunter Memorial Fund.

Rest in peace, John  Hunter (1968-August 28th, 2012). My sincere condolences to his family. Thank you for all your contribution. A great loss to the community.Thank you again.  

After learning the basics of Python, today i will try to implement some basic statistical methods including plotting. We need two important packages mathplotlib and scipy. I remember that there is also numpy library, a bit confused but it's explained very well in official scipy documentation:
"SciPy (pronounced "Sigh Pie") is open-source software for mathematics, science, and engineering. It is also the name of a very popular conference on scientific programming with Python. The SciPy library depends on NumPy, which provides convenient and fast N-dimensional array manipulation. The SciPy library is built to work with NumPy arrays, and provides many user-friendly and efficient numerical routines such as routines for numerical integration and optimization."
i follow two useful blogs in order to learn how to plot and make basic statistical calculation by using pyton, after i learn these topics, i will search about machine learning libraries.




Monday, August 13, 2012

Switching From Perl to Python, Step 3 Python Data Structures

We read the Knuth, so you don't need to
-Tim Peters

After finishing first part of Python, today i decided to read about Python data structures.
Today's topics are:
Night -2-
10.  Modules
11.  Data Structures
12.  Problem Solving

While i was reading about the data structures in Python, list, tuple and dictionary implementations are very similar to corresponding Java collections list, set and map. Please check here to review some examples.

While reading about the dictionaries, defaultdict implementation was interesting, in addition, i really like the one liners, as an example:


myfile=open('names', 'r')
words=[line.rstrip() for line in myfile]
quote='''google
        excite
        yahoo
        bing
        altavista '''
#find the words that exits in file but not in quote
difference=[word for word in quote.split() if word not in words]
print difference

Some useful resources:
Python in High performance computing 
Official python documentation
Data Structures and Algorithms Using Python


Friday, August 10, 2012

Switching From Perl to Python, Step 2 Python Basics

 If you don't know any computer languages, I recommend starting with Python. It is cleanly designed, well documented, and relatively kind to beginners. Despite being a good first language, it is not just a toy; it is very powerful and flexible and well suited for large projects.
How To Become A Hacker, Eric Steven Raymond


From coffeeghost
Following topics are from Byte of Python which is a free Python book for completely beginners.
Today's topics:
Night -1-
1. → Translations
2. → Preface
3. → Introduction
4. → Installation
5. → First Steps
6. → Basics
7. → Operators and Expressions
8. → Control Flow
9. → Functions 

Resources that i have reviewed:

Switching From Perl to Python, Step 1 Which IDE to use for Python programming ?


 Python 2.x is the status quo, Python 3.x is the present and future of the language (http://wiki.python.org/moin/Python2orPython3)


i followed the instruction from vogella, however instead of installing python 2.7 directly from official python web page, i installed from enthought academic version which includes the numpy, Scipy and matplotlib. These modules will be useful when we start programming,
i do not give details for now.


Academic versions of Enthought:
Students or employees from degree-granting institutions may use these installations for an extended period free of cost.


After installing Eclipse and configuration of PyDev , i guess i'm ready for Python. Actually, i'd like to use netbeans instead but netbeans does not have python support after 7.0 versions.

Some experiments to be sure that everything works smoothly:

1-First (little) Python module (from vogella)

2- First (little)NumPy module
3-Scipy and Matplotlib module

Code is from oneau

Ok. then i'm ready for Night 1 for tomorrow:

1. → Translations
2. → Preface
3. → Introduction
4. → Installation
5. → First Steps
6. → Basics
7. → Operators and Expressions
8. → Control Flow
9. → Functions


Sunday, August 5, 2012

Binary Tree based algorithm questions


i will try to find the answers of following 4 algorithm questions which can be implemented using binary search tree (BST). Please refer to the original questions with the Python implementation at Arden's blog.
  • Binary Search Tree Check: Given a binary tree, check whether it’s a binary search tree or not
  • Tree Level Order Print: Given a binary tree of integers, print it in level order. The output will contain space between the numbers in the same level, and new line between different levels.
  • Tree Reverse Level Order Print: This is very similar to the previous post level order print. We again print the tree in level order, but now starting from bottom level to the root.
  • Trim Binary Search Tree: Given the root of a binary search tree and 2 numbers min and max, trim the tree such that all the numbers in the new tree are between min and max (inclusive). The resulting tree should still be a valid binary search tree.
To understand or polish your knowledge about BST, you can go over the great tutorial of Nick Parlenta and for the applications of binary trees you may read the answers posted in SO.

To implement BST in Java, we need to create class like:
 static class TreeNode {

        TreeNode leftReference;
        TreeNode rightReference;
        int nodeValue;

        public TreeNode(int nodeValue) {
            this.nodeValue = nodeValue;
        }
    }

With a given BST, there are 3 kind of walk can be defined, inorder tree walk, preorder tree walk and postorder tree walk. Refer to Wikipedia article to get details. While using inorder tree walk,  note that the BST property allows us to print out all the values in the Binary Search Tree in sorted order. Before, i start implementation we need to understand these terms in order to write the code.

we can implement inorder tree walk for binary search tree check and if BST is not sorted then we conclude that it's a not a BST. Both Tree Level Order Print and Tree Reverse Level Order Print can be implemented in similar way using recursion.

package pkg7binarysearchtreechk;

public class Main {

    static class TreeNode {

        TreeNode leftReference;
        TreeNode rightReference;
        int nodeValue;

        public TreeNode(int nodeValue) {
            this.nodeValue = nodeValue;
        }
    }

    public static void main(String[] args) {
        run();
    }

    public static void run() {
        // tree root node.
        int rootValue = 40;
        TreeNode rootnode = new TreeNode(rootValue);
        System.out.println("root node created, " + rootnode.nodeValue);
        // insertNode new element starting with rootnode.
        insertNode(rootnode, 11);
        insertNode(rootnode, 15);
        insertNode(rootnode, 16);
        insertNode(rootnode, 23);
        insertNode(rootnode, 79);
        
        System.out.println("print the content of  tree in inOrderTree walk");
        printTree(rootnode);
        System.out.println("print the content of  tree in preOrderTree walk");
        printPreOrderTree(rootnode);
        System.out.println("print the content of  tree in  postOrderTree walk");
        printPostOrderTree(rootnode);
    }

    private static void insertNode(TreeNode parentNode, int nodeValue) {
        if (nodeValue < parentNode.nodeValue) {
            if (parentNode.leftReference != null) {
                // Go more depth to left.
                insertNode(parentNode.leftReference, nodeValue);
            } else {
                System.out.println("LEFT: new node value " + nodeValue
                        + " ,its root  " + parentNode.nodeValue);
                parentNode.leftReference = new TreeNode(nodeValue);
            }
        } else if (nodeValue > parentNode.nodeValue) {

            if (parentNode.rightReference != null) {
                // Go more depth to right
                insertNode(parentNode.rightReference, nodeValue);
            } else {
                System.out.println("RIGHT: new node value  " + nodeValue + ", its root " + parentNode.nodeValue);
                parentNode.rightReference = new TreeNode(nodeValue);
            }
        }
    }

    // inorder tree walk
    private static void printTree(TreeNode node) {
        int comparison;
        if (node != null) {
            printTree(node.leftReference);
            comparison = node.nodeValue;
            if (comparison < node.nodeValue) {
                System.out.println("Error not BST");
            }
            System.out.println("node value  " + node.nodeValue);
            printTree(node.rightReference);
        }
    }
    
  // preorder tree walk 
    private static void printPreOrderTree(TreeNode node) {
        if (node != null) {
            System.out.println("node value  " + node.nodeValue);
            printTree(node.leftReference);
            printTree(node.rightReference);
        }
    }
  // postorder tree walk
     private static void printPostOrderTree(TreeNode node) {
        if (node != null) {
            printTree(node.leftReference);
            printTree(node.rightReference);
            System.out.println("node value  " + node.nodeValue);
        }
    }
}