Gentle Introduction To Sparse Matrix For Machine Learning In 2021


A sparse matrix is normal in ML or Machine Learning. While they happen normally in some data collection measures, all the more regularly they emerge while applying certain data change strategies like: 

  1. TfidfVectorizing
  2. CountVectorizing
  3. One-hot encoding

Turns out there are 2 significant kinds of matrices: 

  1. Sparse matrices have lots of ZERO (0) values.
  2. Dense matrices don’t.
  1. Sparse Matrix
  2. Problems with Sparsity
  3. Sparse Matrices in Machine Learning
  4. Working with Sparse Matrices
  5. Sparse Matrices in Python

1. Sparse Matrix

In scientific computing and numerical analysis, a sparse array or sparse matrix is a matrix where a large portion of the components are zero. There is no precise meaning of the number of components that should be zero for a matrix to be viewed as sparse, yet a typical measure is that the number of non-zero components is generally the number of columns or rows.

A sparse array is an array of data where numerous components have an estimation of zero value. This is as opposed to a dense array, where the vast majority of the components have non-zero values or are “full” of numbers.

Sparsity = Count zero components divided by Total components.

The following is a little 3 x 7 sparse matrix example:

[1, 0, 3, 4, 5, 7, 7

2, 0, 0, 0, 4, 0, 5

4, 2, 4, 4, 0, 1, 0]

The sparse matrix example has 7 zero values of the 21 components in the matrix, giving this matrix a sparsity score of 0.333 or about 33.33 %.

2. Problems with Sparsity

Sparse matrices can make issues with respects to time and space complexity.

  1. Time Complexity: Assuming an enormous sparse matrix can be found a way into memory, we will need to perform the procedure on this matrix. Basically, if the matrix generally contains zero-values, for example, no information, at that point, performing tasks across this matrix may take quite a while where the majority of the calculation performed will include adding or increasing zero values together.
  2. Space Complexity: Very huge sparse matrices require a ton of memory, and some huge matrices that we wish to work with are sparse. An illustration of an extremely huge matrix that is too enormous to even consider being put away in memory is a link matrix that shows the links starting with one site then onto the next.

3. Sparse Matrices in Machine Learning

Sparse matrix turns up a ton in applied ML. In this segment, we will take some normal guides to spur you to know about the issues of sparsity. 

1. Areas of Study:

A few areas of study inside ML should create specific strategies to address sparsity straightforwardly as the information is quite often sparse. 

Examples are: 

  1. Common language preparing for working with reports of text.
  2. Recommender frameworks for working with item use inside an inventory.

2. Data Preparation:

Sparse matrix comes up in encoding plans utilized in the planning of data.

Examples are: 

  1. The one-hot encoding used to address absolute data as sparse binary vectors.
  2. TF-IDF encoding utilised to address frequency word recurrence scores in the document.

3. Data:

Sparse matrices come up in some particular sorts of data, most quiet perceptions that record the event or check of a movement. 

Examples are:

  1. Regardless of whether a client has watched a film in a film list.
  2. Regardless of whether a client has bought an item in an item list.

4. Working with Sparse Matrices

Sparse data implies that there are numerous gaps present in the data being recorded. 

Different data designs can be utilized to effectively build a sparse matrix; 3 normal models are recorded below:

  1. Coordinate List
  2. List of Lists
  3. Dictionary of Keys

Some data structures are more appropriate for performing proficient sparse matrix operations; 3 regularly utilized models are recorded below: 

  1. Sparse Matrix Arithmetic
  2. Conversion Functions
  3. Compressed Row Storage

5. Sparse Matrices in Python

SciPy gives apparatuses for making sparse matrices utilizing various data structures, just as devices for changing a dense matrix over to a sparse matrix. It is an open-source and free Python library utilized for technical computing and scientific computing. 

Both SciPy vs. NumPy are modules of Python, and they are utilized for different activities of the data. Then again, SciPy contains all the mathematical functions, some of which are there in NumPy somewhat and not in undeniable structure.

A dense matrix put away in a NumPy array can be changed over into a sparse matrix utilizing the CSR matrix portrayal by calling the csr_matrix () function.

For instance, consider a matrix of size 5 X 6 containing 6 number of non-zero values. This sparse matrix representation as demonstrated in the table below:

[0, 0, 0, 0, 9, 0

0, 8, 0, 0, 0, 0

4, 0, 0, 2, 0, 0

0, 0, 0, 0, 0, 5

0, 0, 2, 0, 0, 0]

5 6 6
0 4 9
1 1 8
2 0 4
2 3 2
3 5 5
4 2 2

In the above model network, there are just 6 non-zero components (those are 2, 5, 2, 4, 8, and 9) and the matrix size is 5 X 6. 

Here the principal row in the right-side table is loaded up with values 6, 6 and 5, which shows that it is a sparse matrix with 6 non-zero values, 6 columns, and 5 rows.

The application of sparse matrix is for figuring huge scope applications that dense matrices can’t deal with.

  • Types of the sparse matrix:
  1. Row-based list of lists sparse matrix
  2. Dictionary of keys based sparse matrix
  3. Sparse matrix with diagonal storage
  4. Compressed Sparse Row matrix
  5. Compressed Sparse Column matrix
  6. A sparse matrix in coordinate format
  7. Block Sparse Row matrix


The advantages of the sparse matrix are to store data that contains an enormous number of zero-valued components can both save a lot of memory and accelerate the preparing of that data.

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