mathjs/src/function/matrix/filter.js

import { filter, filterRegExp } from '../../utils/array'
import { maxArgumentCount } from '../../utils/function'
import { factory } from '../../utils/factory'

const name = 'filter'
const dependencies = ['typed']

export const createFilter = /* #__PURE__ */ factory(name, dependencies, ({ typed }) => {
  /**
   * Filter the items in an array or one dimensional matrix.
   *
   * Syntax:
   *
   *    math.filter(x, test)
   *
   * Examples:
   *
   *    function isPositive (x) {
   *      return x > 0
   *    }
   *    math.filter([6, -2, -1, 4, 3], isPositive) // returns [6, 4, 3]
   *
   *    math.filter(["23", "foo", "100", "55", "bar"], /[0-9]+/) // returns ["23", "100", "55"]
   *
   * See also:
   *
   *    forEach, map, sort
   *
   * @param {Matrix | Array} x    A one dimensional matrix or array to filter
   * @param {Function | RegExp} test
   *        A function or regular expression to test items.
   *        All entries for which `test` returns true are returned.
   *        When `test` is a function, it is invoked with three parameters:
   *        the value of the element, the index of the element, and the
   *        matrix/array being traversed. The function must return a boolean.
   * @return {Matrix | Array} Returns the filtered matrix.
   */
  return typed('filter', {
    'Array, function': _filterCallback,

    'Matrix, function': function (x, test) {
      return x.create(_filterCallback(x.toArray(), test))
    },

    'Array, RegExp': filterRegExp,

    'Matrix, RegExp': function (x, test) {
      return x.create(filterRegExp(x.toArray(), test))
    }
  })
})

/**
 * Filter values in a callback given a callback function
 * @param {Array} x
 * @param {Function} callback
 * @return {Array} Returns the filtered array
 * @private
 */
function _filterCallback (x, callback) {
  // figure out what number of arguments the callback function expects
  const args = maxArgumentCount(callback)

  return filter(x, function (value, index, array) {
    // invoke the callback function with the right number of arguments
    if (args === 1) {
      return callback(value)
    } else if (args === 2) {
      return callback(value, [index])
    } else { // 3 or -1
      return callback(value, [index], array)
    }
  })
}