Categorization using Neural Networks

Fatai Salami showed the audience how to implement categorization using Neural Networks.

Transcript

1. Categorization using Neural Networks by Fatai Salami (Phatye)
2. • Fatai Salami • Software Developer – Lecturer – Researcher • fatai.salami@gmail.com or @phatye Profile
3. • Sometimes referred to as classification • categorization is assigning a category ci to document di What is Categorization
4. • text categorization (e.g., spam filtering) • fraud detection • optical character recognition • machine vision (e.g., face detection) • natural-language processing (e.g., spoken language understanding) • market segmentation (e.g.: predict if customer will respond to promotion) • Bioinformatics (e.g., classify proteins according to their function) Categorization Tasks
5. • IT DEPENDS • How large is your training set?, How large is your feature space? Data Set linearly separable? • Quality data trumps everything What Algorithm should I use?
6. Case Study: Will s/he run away with my money?
7. • Clean data • Identify possible features • Separate data in the ratio 60 (train) : 20 (validate) : 20 (test) Getting data
8. • Organization • State of residence • Area of residence • Monthly income • Gender • Marital status • No of dependants • How much borrowed? • Account balance at middle of the month • Credit score etc… Identify features
9. Good to have all features in the range -1 to +1 • numeric x-data can be Gaussian normalized (really depends on your data) • binary x-data is (-1 +1) encoded • categorical x-data is 1-of-(C-1) effects-coded ( ex: [0,1] or [1,0] or [-1,-1] ) Prepare features for Neural Network
10. • numeric y-data is left alone • binary y-data is 1-of-C dummy-coded • categorical y-data is 1-of-C dummy-coded
11. Design Neural Network Model
12. • Input layer – only one layer. Neurons determined by number of features to be used • Output layer – only one layer. Usually one neuron except for multiclass classification (run away: 0, return money: 1) Introducing “maybe” = 3 neurons (run away: {1,0,0}, maybe: {0,1,0}, return money:{0,0,1}
13. • Hidden layers – linearly separable data requires no hidden layer. Rare problems requiring more than two hidden layer. One is usually enough. There are many rule-of-thumb methods: • The number of hidden neurons should be between the size of the input layer and the size of the output layer. • The number of hidden neurons should be 2/3 the size of the input layer, plus the size of the output layer. • The number of hidden neurons should be less than twice the size of the input layer.
14. • Too few hidden neurons result in under-fitting (model is not able to get good results) • Too many hidden neurons results in over-fitting (model fits well with training data but does not perform well with test data)
15. Always better to use existing library/services • Azure machine learning services • Weka • C# - Aforge.Net, NeuronDotNet • Java – Neuroph • Python – PyBrain, NeuroLab • Php - Neural Mesh • R - nnet Coding the Neural Network
16. • Epoch – number of iterations (too much can result to model over-fitting) • Learning rate – how much an updating step influences the current value of the weights (too small – runs for long; too large – can go past optimum weights) • Momentum – used to diminish the fluctuations in weight changes over consecutive iterations Network Configuration Terms
17. Training using Aforge.Net
18. Predicting using Aforge.Net
19. • Analysing the result
20. Where: • Vi = Original output of data • Vo = Output from neural net • Vl = length of data • TP = True Positive – accurately predicted valid for a valid transaction. • FP = False Positive – predicted valid for a fraudulent transaction. • FN = False Negative – predicted fraudulent for a valid transaction.
21. Thank you