matrix-magic

npm install --save matrix-magic

This library performs various transformations on matrices. This library does not do matrix operations (or more specifically, matrix multiplication), but serves to manipulate the shape of a matrix. It does stuff like this:

getMajorDiagonals()

[[a, b, c],         [[e],
 [d, a, b],   -->    [d, d],
 [e, d, a]]          [a, a, a],
                     [b, b],
                     [c]]

Here's another fun one:

getClockwiseSpiral()

[[1, 2, 3],         
 [8, 9, 4],   -->  [1, 2, 3, 4, 5, 6, 7, 8, 9]
 [7, 6, 5]]

It also provides some utilities to work with matrices:

transpose()

[[a, b, c],          [[a, a, a],
 [a, b, c],   -->     [b, b, b],
 [a, b, c]]           [c, c, c]]

getMiddleCols()

[[*, 1, 2, 3, *],          [[1, 2, 3],
 [*, 4, 5, 6, *],    -->    [4, 5, 6],
 [*, 7, 8, 9, *]]           [7, 8, 9]]

Library

Note that in the following functions, matrix is an array of arrays, where each sub-array has the same length. Most of these functions will throw an error if the input is not a matrix.

Matrix Utilities <>

getMatrixWidth(matrix)

Returns the width of matrix i.e. the number of columns.

getMatrixHeight(matrix)

Returns the height of matrix i.e. the number of rows.

getMatrixDimensions(matrix)

Returns and object {width, height}, where width is the number of columns in matrix, and height is the number of rows in matrix.

Row Utilities <>

sliceMatrixRows(matrix, start, stop)

Returns the slice of the rows of matrix from index start to index stop - 1, much like Array.prototype.slice().

getTopRow(matrix)

Returns the top row of matrix as a matrix.

getAllButTopRow(matrix)

Returns matrix without the top row.

getBottomRow(matrix)

Returns the bottom row of matrix as a matrix.

getAllButBottomRow(matrix)

Returns matrix without the bottom row.

getMiddleRows(matrix)

Returns matrix without top and bottom rows.

flipRows(matrix) <>

Returns matrix with the rows in reverse order.

Column Utilities <>

sliceMatrixCols(matrix, start, stop)

Returns the slice of the columns of matrix from index start to index stop - 1, much like Array.prototype.slice().

getLeftCol(matrix)

Returns the left column of matrix as a matrix.

getRightCol(matrix)

Returns the right column of `matrix as a matrix.

getAllButLeftCol(matrix)

Returns matrix without the left column.

getAllButRightCol(matrix)

Returns matrix without the right column.

getMiddleCols(matrix)

Returns matrix without the left and right columns.

flipCols(matrix) <>

Returns matrix with the columns in reverse order.

Matrix Utilities

transpose(matrix) <>

Returns matrix with the rows and the columns flipped, i.e. the leftmost column is now the top row (and vice versa), and so on.

getMinorDiagonals(matrix) <>

Returns an nArray (an array of arrays, not necessarily of equal length) of the minor diagonals of matrix, starting from the top-left corner, down to the bottom-right corner.

getMajorDiagonals(matrix) <>

Returns an nArray (an array of arrays, not necessarily of equal length) of the major diagonals of matrix, starting from the bottom-left corner, up to the top-right corner.

getClockwiseSpiral(matrix) <>

Returns an array of the entries of matrix going clockwise from the top-left corner, spiraling into the center.

getCounterClockwiseSpiral(matrix) <>

Returns an array of entries of matrix going counter-clockwise from the top-left corner, spiraling into the center.

Decorators <>

doColumnOperation(fcn)(matrix, ...args)

doColumnOperation(fcn) returns a function that transposes matrix, applies fcn, and then returns the resulting transpose.

This utility allows us to use row utilities on the columns. The definition is

const doColumnOperation = fcn => (mtx, ...args) => {
  return transpose(fcn(transpose(mtx), ...args));
};

doMatrixCheck(fcn)(nArray, ...args)

doMatrixCheck(fcn) returns a function that evaluates fcn(nArray, ...args) if nArray is a matrix. If nArray is not a matrix, it will throw an error.

matrixWrapper(fcn)(nArray, ...args)

matrixWrapper(fcn) returns a function that evaluates fcn(nArray, ...args) pending several checks. Those checks are:

• Check if it is the empty matrix [[]]
• Check if it is a matrix with doMatrixCheck

About

This library has no dependencies and consists of entirely pure functions. I mostly did this because I thought it would be fun (and it is!), and to learn about unit testing with jest.

If you'd like to contribute, then by all means, go ahead! Here are ways you can help out:

• Make snippets like the ones I made above to show what each function is doing.
• Contribute to the documentation! Describe what each function does (related to providing examples).
• Write a test! This would be a big help, and would be a great way to get into testing if you have yet to try it (and you should be testing your code).
• Re-write a test. Just because it's there doesn't mean it's a good test.
• Make a pull request for a new feature. This might be a little harder, as I'd like to adhere to a purely functional style. Talk to me if you're interested in adding something.
• Find and report bugs!