mathjs/src/function/matrix/matrixFromColumns.js

import { factory } from '../../utils/factory.js'

const name = 'matrixFromColumns'
const dependencies = ['typed', 'matrix', 'flatten', 'size']

export const createMatrixFromColumns = /* #__PURE__ */ factory(name, dependencies, ({ typed, matrix, flatten, size }) => {
  /**
   * Create a dense matrix from vectors as individual columns.
   * If you pass row vectors, they will be transposed (but not conjugated!)
   *
   * Syntax:
   *
   *    math.matrixFromColumns(...arr)
   *    math.matrixFromColumns(col1, col2)
   *    math.matrixFromColumns(col1, col2, col3)
   *
   * Examples:
   *
   *    math.matrixFromColumns([1, 2, 3], [[4],[5],[6]])
   *    math.matrixFromColumns(...vectors)
   *
   * See also:
   *
   *    matrix, matrixFromRows, matrixFromFunction, zeros
   *
   * @param {... Array | Matrix} cols Multiple columns
   * @return { number[][] | Matrix } if at least one of the arguments is an array, an array will be returned
   */
  return typed(name, {
    '...Array': function (arr) {
      return _createArray(arr)
    },
    '...Matrix': function (arr) {
      return matrix(_createArray(arr.map(m => m.toArray())))
    }

    // TODO implement this properly for SparseMatrix
  })

  function _createArray (arr) {
    if (arr.length === 0) throw new TypeError('At least one column is needed to construct a matrix.')
    const N = checkVectorTypeAndReturnLength(arr[0])

    // create an array with empty rows
    const result = []
    for (let i = 0; i < N; i++) {
      result[i] = []
    }

    // loop columns
    for (const col of arr) {
      const colLength = checkVectorTypeAndReturnLength(col)

      if (colLength !== N) {
        throw new TypeError('The vectors had different length: ' + (N | 0) + ' ≠ ' + (colLength | 0))
      }

      const f = flatten(col)

      // push a value to each row
      for (let i = 0; i < N; i++) {
        result[i].push(f[i])
      }
    }

    return result
  }

  function checkVectorTypeAndReturnLength (vec) {
    const s = size(vec)

    if (s.length === 1) { // 1D vector
      return s[0]
    } else if (s.length === 2) { // 2D vector
      if (s[0] === 1) { // row vector
        return s[1]
      } else if (s[1] === 1) { // col vector
        return s[0]
      } else {
        throw new TypeError('At least one of the arguments is not a vector.')
      }
    } else {
      throw new TypeError('Only one- or two-dimensional vectors are supported.')
    }
  }
})