Exploration of Recommendation Systems

Dataset Used
Tools Used
Hyperparameters Used
Data-Preprocessing
Experiments
Results
What we learned?
References :

Dataset Used

Books Recommendation Dataset
Artificial Dataset

Tools Used

Python Programming language to perform experiments.
Used Sklearn for Modelling SVD.
Used Gridsearch for performing hyperparameter tuning.
Used matplotlib library to build various plots to analyze and showcase the results of experiments.
Pandas and Numpy to perform data-preprocessing

Hyperparameters Used

Training and Testing Split: 80%, 20%
num_of_components or top ‘r’ singular values =250
iterations=20

Data-Preprocessing

Dataset is 97% sparse.

Ratings: (1-10)

Final Shape (500, 551) –> (Users, Books) Rating Matrix

Ensured the Users have at least rated more than 300 books
Ensured the Books had at least 50 ratings from users
Fill Empty/NAN(Not a Number) values with zeros.
Remove duplicates(ensures unique users and books)

Experiments

Experiment 1: Finding Best Filling Method for Dealing with Missing Values in Sparse Matrix

1. Step 1: Create the User-Book Sparse matrix : Fill unknowns with:

zeroes
column mean per user
row mean per book
column median per user
row median per book

2. Step 2: Singular Value Decomposition (SVD): Perform SVD on the sparse matrix attained from Step 1 and get a low rank Approximation by using a fraction of the components (250, acquired through cross-validation) to reconstruct the User-Book Matrix

3. Step 3: Evaluate Results at every iteration Compare predicted reconstructed matrix & original matrix using RMSE, MSE, MAE, Pearson Coefficient, & Cosine Similarity

4. Step 4: Replace with original values : Substitute the known non-zero values of the original sparse matrix into the output matrix and left the rest untouched.

5. Go to Step 2 and repeat for 5 iterations.

Experiment 2: Increasing Sparsity

1. Step 1: Increase Sparsity- Set 300 random elements in the User-Book Sparse Matrix to zero

2. Step 2: Predict- Perform SVD & use a fraction of components (250 components(acquired through Cross Validation)) on the final sparse matrix from the above step to get the reconstructed matrix.

3. Step 3: Replace with original values- Substitute the known elements of the original sparse matrix into output matrix, but leave the rest untouched.

4. Step 4: Evaluate Results- Compare prediction matrix & original matrix using RMSE, MSE, MAE, Pearson Coefficient, & Cosine Similarity

5. Decreasing Sparsity Test- Repeat all the steps 2, 3, 4, 5 by First Filling 300 unknown values with mean (column wise)

Experiment 3: Artificial Dataset Creation

1. Create low-rank (250 components) reconstruction using SVD from Books-Users sparse matrix. (iterations=1)

2. Add zero-mean gaussian random noise to every element.

3. Round up to nearest integers in range 1-10.

4. Randomly drop 20% of rows & columns.

5. Increasing the sparsity on artificial dataset- Increase sparsity by 10% in every iteration (randomly setting elements to zero)

6. Perform SVD and evaluate the results.

Algorithim Used :

Results

Experiment 1: Iterative Results of SVD Recommender Prediction Algorithm using Different Filling Methods(Iterations =5)

Experiment 2: Increasing & Decreasing Sparsity on User-Books Sparse Matrix(Iterations =20)

Experiment 3: Increasing Sparsity on Artifical Dataset in Range 0% - 90%

What we learned?

As the user-item dataset matrix becomes sparser, the recommendations become less accurate
Different strategies to fill in unknown values in the user-item matrix
Iterative SVD algorithm for recommendation