Welcome to the second project of the Machine Learning Engineer Nanodegree! In this notebook, some template code has already been provided for you, and it will be your job to implement the additional functionality necessary to successfully complete this project. Sections that begin with 'Implementation' in the header indicate that the following block of code will require additional functionality which you must provide. Instructions will be provided for each section and the specifics of the implementation are marked in the code block with a 'TODO' statement. Please be sure to read the instructions carefully!
In addition to implementing code, there will be questions that you must answer which relate to the project and your implementation. Each section where you will answer a question is preceded by a 'Question X' header. Carefully read each question and provide thorough answers in the following text boxes that begin with 'Answer:'. Your project submission will be evaluated based on your answers to each of the questions and the implementation you provide.
Note: Code and Markdown cells can be executed using the Shift + Enter keyboard shortcut. In addition, Markdown cells can be edited by typically double-clicking the cell to enter edit mode.
Answer:
It is clearly a classification problem, because we need a clear discrete answer: yes or no.
Classification can answer to a question: do wee need to intervent - yes or no, while regression gives us a continuous answer, which clearly isn't required here.
In [2]:
# Import libraries
import numpy as np
import pandas as pd
from time import time
from sklearn.metrics import f1_score
# Read student data
student_data = pd.read_csv("student-data.csv")
print "Student data read successfully!"
Let's begin by investigating the dataset to determine how many students we have information on, and learn about the graduation rate among these students. In the code cell below, you will need to compute the following:
n_students.n_features.n_passed.n_failed.grad_rate, in percent (%).
In [3]:
# Calculate number of students
n_students = len(student_data.index)
# Calculate number of features (minus 1, because "passed" is not a feature, but a target column)
n_features = len(student_data.columns) - 1
# Calculate passing students
n_passed = len(student_data[student_data['passed'] == 'yes'])
# Calculate failing students
n_failed = len(student_data[student_data['passed'] == 'no'])
# Calculate graduation rate
grad_rate = (n_passed / float(n_students)) * 100
# Print the results
print "Total number of students: {}".format(n_students)
print "Number of features: {}".format(n_features)
print "Number of students who passed: {}".format(n_passed)
print "Number of students who failed: {}".format(n_failed)
print "Graduation rate of the class: {:.2f}%".format(grad_rate)
In this section, we will prepare the data for modeling, training and testing.
It is often the case that the data you obtain contains non-numeric features. This can be a problem, as most machine learning algorithms expect numeric data to perform computations with.
Run the code cell below to separate the student data into feature and target columns to see if any features are non-numeric.
In [4]:
# Extract feature columns
feature_cols = list(student_data.columns[:-1])
# Extract target column 'passed'
target_col = student_data.columns[-1]
# Show the list of columns
print "Feature columns:\n{}".format(feature_cols)
print "\nTarget column: {}".format(target_col)
# Separate the data into feature data and target data (X_all and y_all, respectively)
X_all = student_data[feature_cols]
y_all = student_data[target_col]
# Show the feature information by printing the first five rows
print "\nFeature values:"
print X_all.head()
As you can see, there are several non-numeric columns that need to be converted! Many of them are simply yes/no, e.g. internet. These can be reasonably converted into 1/0 (binary) values.
Other columns, like Mjob and Fjob, have more than two values, and are known as categorical variables. The recommended way to handle such a column is to create as many columns as possible values (e.g. Fjob_teacher, Fjob_other, Fjob_services, etc.), and assign a 1 to one of them and 0 to all others.
These generated columns are sometimes called dummy variables, and we will use the pandas.get_dummies() function to perform this transformation. Run the code cell below to perform the preprocessing routine discussed in this section.
In [5]:
def preprocess_features(X):
''' Preprocesses the student data and converts non-numeric binary variables into
binary (0/1) variables. Converts categorical variables into dummy variables. '''
# Initialize new output DataFrame
output = pd.DataFrame(index = X.index)
# Investigate each feature column for the data
for col, col_data in X.iteritems():
# If data type is non-numeric, replace all yes/no values with 1/0
if col_data.dtype == object:
col_data = col_data.replace(['yes', 'no'], [1, 0])
# If data type is categorical, convert to dummy variables
if col_data.dtype == object:
# Example: 'school' => 'school_GP' and 'school_MS'
col_data = pd.get_dummies(col_data, prefix = col)
# Collect the revised columns
output = output.join(col_data)
return output
X_all = preprocess_features(X_all)
print "Processed feature columns ({} total features):\n{}".format(len(X_all.columns), list(X_all.columns))
So far, we have converted all categorical features into numeric values. For the next step, we split the data (both features and corresponding labels) into training and test sets. In the following code cell below, you will need to implement the following:
X_all, y_all) into training and testing subsets.random_state for the function(s) you use, if provided.X_train, X_test, y_train, and y_test.
In [6]:
# Import Cross Validation functionality to perform splitting the data
from sklearn import cross_validation
# Set the number of training points
num_train = 300
# Set the number of testing points
num_test = X_all.shape[0] - num_train
# Calculate split percentage
splitPercentage = float(num_test) / (num_train + num_test)
print "Split percentage: {0:.2f}% ".format(splitPercentage * 100)
# Shuffle and split the dataset into the number of training and testing points above
X_train, X_test, y_train, y_test = cross_validation.train_test_split(
X_all, y_all, test_size = splitPercentage, stratify = y_all, random_state = 0)
# Show the results of the split
print "Training set has {} samples.".format(X_train.shape[0])
print "Testing set has {} samples.".format(X_test.shape[0])
In this section, you will choose 3 supervised learning models that are appropriate for this problem and available in scikit-learn. You will first discuss the reasoning behind choosing these three models by considering what you know about the data and each model's strengths and weaknesses. You will then fit the model to varying sizes of training data (100 data points, 200 data points, and 300 data points) and measure the F1 score. You will need to produce three tables (one for each model) that shows the training set size, training time, prediction time, F1 score on the training set, and F1 score on the testing set.
Answer:
As we need to get a binary answer, it is better to choose among methods which are used for binary classification more often. I've chosen three learning models: K Nearest Neighbors, Logistic Regression and Support Vector Machine.
K Nearest Neighbors is one the simplest ML algorithms:
Real-World Applications:
Advantages:
Disadvantages:
Logistic Regression:
Real-World Applications:
Advantages:
Disadvantages:
Support Vector Machine:
Real-World Applications:
Advantages:
Disadvantages:
Reasons to choose these algorithms:
Run the code cell below to initialize three helper functions which you can use for training and testing the three supervised learning models you've chosen above. The functions are as follows:
train_classifier - takes as input a classifier and training data and fits the classifier to the data.predict_labels - takes as input a fit classifier, features, and a target labeling and makes predictions using the F1 score.train_predict - takes as input a classifier, and the training and testing data, and performs train_clasifier and predict_labels.
In [7]:
def train_classifier(clf, X_train, y_train):
''' Fits a classifier to the training data. '''
# Start the clock, train the classifier, then stop the clock
start = time()
clf.fit(X_train, y_train)
end = time()
# Print the results
print "Trained model in {:.4f} seconds".format(end - start)
def predict_labels(clf, features, target):
''' Makes predictions using a fit classifier based on F1 score. '''
# Start the clock, make predictions, then stop the clock
start = time()
y_pred = clf.predict(features)
end = time()
# Print and return results
print "Made predictions in {:.4f} seconds.".format(end - start)
return f1_score(target.values, y_pred, pos_label='yes')
def train_predict(clf, X_train, y_train, X_test, y_test):
''' Train and predict using a classifer based on F1 score. '''
# Indicate the classifier and the training set size
print "Training a {} using a training set size of {}. . .".format(clf.__class__.__name__, len(X_train))
# Train the classifier
train_classifier(clf, X_train, y_train)
# Print the results of prediction for both training and testing
print "F1 score for training set: {:.4f}.".format(predict_labels(clf, X_train, y_train))
print "F1 score for test set: {:.4f}.".format(predict_labels(clf, X_test, y_test))
With the predefined functions above, you will now import the three supervised learning models of your choice and run the train_predict function for each one. Remember that you will need to train and predict on each classifier for three different training set sizes: 100, 200, and 300. Hence, you should expect to have 9 different outputs below — 3 for each model using the varying training set sizes. In the following code cell, you will need to implement the following:
clf_A, clf_B, and clf_C.random_state for each model you use, if provided.X_train and y_train.
In [21]:
# Import the three supervised learning models from sklearn
# Logistic Regression
from sklearn.linear_model import LogisticRegression
# Support Vector Machine
from sklearn.svm import SVC
# KNN classifier
from sklearn.neighbors import KNeighborsClassifier
# Random State for each model consistent with splitting Random State = 0
randState = 0
# Initialize the three models
clf_A = LogisticRegression(random_state = randState)
clf_B = SVC(random_state = randState)
clf_C = KNeighborsClassifier()
classifiers = [clf_A, clf_B, clf_C]
# Set up the training set sizes
X_train_100 = X_train[:100]
y_train_100 = y_train[:100]
X_train_200 = X_train[:200]
y_train_200 = y_train[:200]
X_train_300 = X_train
y_train_300 = y_train
trainingData = [(X_train_100, y_train_100), (X_train_200, y_train_200), (X_train_300, y_train_300)]
# Execute the 'train_predict' function for each classifier and each training set size
for each in range(len(classifiers)):
print classifiers[each]
print "-------------------"
for data in trainingData:
train_predict(classifiers[each], data[0], data[1], X_test, y_test)
print
Edit the cell below to see how a table can be designed in Markdown. You can record your results from above in the tables provided.
Classifer 1 - Logistic Regression
| Training Set Size | Training Time | Prediction Time (test) | F1 Score (train) | F1 Score (test) |
|---|---|---|---|---|
| 100 | 0.0077 | 0.0012 | 0.8759 | 0.7500 |
| 200 | 0.0041 | 0.0005 | 0.8532 | 0.8085 |
| 300 | 0.0050 | 0.0002 | 0.8402 | 0.7770 |
Classifer 2 - Support Vector Machine
| Training Set Size | Training Time | Prediction Time (test) | F1 Score (train) | F1 Score (test) |
|---|---|---|---|---|
| 100 | 0.0016 | 0.0008 | 0.8919 | 0.7737 |
| 200 | 0.0036 | 0.0019 | 0.8795 | 0.8182 |
| 300 | 0.0080 | 0.0029 | 0.8664 | 0.8289 |
Classifer 3 - K Nearest Neighbors
| Training Set Size | Training Time | Prediction Time (test) | F1 Score (train) | F1 Score (test) |
|---|---|---|---|---|
| 100 | 0.0019 | 0.0024 | 0.8592 | 0.7910 |
| 200 | 0.0013 | 0.0016 | 0.8425 | 0.7941 |
| 300 | 0.0011 | 0.0039 | 0.8688 | 0.7714 |
In this final section, you will choose from the three supervised learning models the best model to use on the student data. You will then perform a grid search optimization for the model over the entire training set (X_train and y_train) by tuning at least one parameter to improve upon the untuned model's F1 score.
Based on the experiments you performed earlier, in one to two paragraphs, explain to the board of supervisors what single model you chose as the best model. Which model is generally the most appropriate based on the available data, limited resources, cost, and performance?
Answer:
After the data stratification we immediately get better results from the SVM, but it takes much longer to predict.
The best model in terms of cost and efficiency for this data is probably a Logistic Regression. Scores are consistent and the classificator works blazingly fast, while the difference in scores with the SVM is not huge.
Answer:
Logistic Regression takes the data and tries to calculate the probability of occurence of an event by fitting data on a logistic curve. It takes available information about previous students and if they passed or not, and then tries to calculate the probability of another student to pass the exams given the data.
Training:
As an example, if we wanted to predict success of students in their life, based on their scores, we would develop something called a model using training data.
We have scores (independent variable), we also know whether a person succeeded or not (dependent variable). We come up with some predictions and then look at how close our predictions were with the recorded data.
If we predicted 0.9 on someone (who succeded in his\her life), and in the same manner we are pretty close in all our predictions then we have a very developed and a good model. If we missed the correct answer, we would go about looking at various models (something called minimizing the squared error: we take a look at sum of errors for each prediction in each model and try to see if we can go even lower than it) and find out the model which fits very closely with our recorded data.
Predicting:
Then we can plug other people data scores into this model and it returns a number between 0 and 1. By looking at it, if it is greater than 0.5 -> a person is successful, or if it is lower than 0.5 -> person is unsuccessful.
Fine tune the chosen model. Use grid search (GridSearchCV) with at least one important parameter tuned with at least 3 different values. You will need to use the entire training set for this. In the code cell below, you will need to implement the following:
sklearn.grid_search.gridSearchCV and sklearn.metrics.make_scorer.parameters = {'parameter' : [list of values]}.clf.make_scorer and store it in f1_scorer.pos_label parameter to the correct value!clf using f1_scorer as the scoring method, and store it in grid_obj.X_train, y_train), and store it in grid_obj.
In [41]:
# Import 'GridSearchCV' and 'make_scorer'
from sklearn.metrics import make_scorer
from sklearn.grid_search import GridSearchCV
def gridSearch(clf, parameters):
# Make an f1 scoring function using 'make_scorer'
f1_scorer = make_scorer(f1_score, pos_label="yes")
# Perform grid search on the classifier using the f1_scorer as the scoring method
grid_obj = GridSearchCV(clf, parameters, scoring=f1_scorer)
# Fit the grid search object to the training data and find the optimal parameters
grid_obj = grid_obj.fit(X_train, y_train)
# Get the estimator
clf = grid_obj.best_estimator_
return clf
# Create the parameters list you wish to tune
svcParameters = [
{'C': [1, 10, 100], 'kernel': ['rbf'], 'gamma': ['auto']},
{'C': [1, 10, 100, 1000], 'kernel': ['linear', 'rbf', 'poly']}
]
knnParams = {'n_neighbors': [2, 3, 4, 5],
'weights': ['uniform', 'distance']}
regresParams = {'C': [0.5, 1.0, 10.0, 100.0],
'max_iter': [100, 1000],
'solver': ['sag', 'liblinear']}
randState = 0
classifiers = [gridSearch(SVC(random_state = randState), svcParameters),
gridSearch(KNeighborsClassifier(), knnParams),
gridSearch(LogisticRegression(random_state = randState), regresParams)]
# Report the final F1 score for training and testing after parameter tuning
# I've tested all three of them just out of curiosity, I've chosen Logistic Regression initially.
for clf in classifiers:
print clf
print "Tuned model has a training F1 score of {:.4f}.".format(predict_labels(clf, X_train, y_train))
print "Tuned model has a testing F1 score of {:.4f}.".format(predict_labels(clf, X_test, y_test))
print "-----------------"
Answer:
Tuned Logistic Regression is much faster than SVM, better than KNN in score and has an improvement of 2% in score after tuning:
Note: Once you have completed all of the code implementations and successfully answered each question above, you may finalize your work by exporting the iPython Notebook as an HTML document. You can do this by using the menu above and navigating to
File -> Download as -> HTML (.html). Include the finished document along with this notebook as your submission.