mathjs/lib/function/arithmetic/subtract.js

'use strict';

var typed = require('typed-function');
var util = require('../../util/index');

var BigNumber = require('decimal.js');
var Complex = require('../../type/Complex');
var Matrix = require('../../type/Matrix');
var Unit = require('../../type/Unit');
var collection = require('../../type/collection');

var toBigNumber= util.bignumber.toBigNumber;
var isBoolean = util['boolean'].isBoolean;
var isNumber = util.number.isNumber;
var isComplex = Complex.isComplex;
var isUnit = Unit.isUnit;
var isCollection = collection.isCollection;

// TODO: replace subtract with a typed function

/**
 * Subtract two values, `x - y`.
 * For matrices, the function is evaluated element wise.
 *
 * Syntax:
 *
 *    math.subtract(x, y)
 *
 * Examples:
 *
 *    math.subtract(5.3, 2);        // returns Number 3.3
 *
 *    var a = math.complex(2, 3);
 *    var b = math.complex(4, 1);
 *    math.subtract(a, b);          // returns Complex -2 + 2i
 *
 *    math.subtract([5, 7, 4], 4);  // returns Array [1, 3, 0]
 *
 *    var c = math.unit('2.1 km');
 *    var d = math.unit('500m');
 *    math.subtract(c, d);          // returns Unit 1.6 km
 *
 * See also:
 *
 *    add
 *
 * @param  {Number | BigNumber | Boolean | Complex | Unit | Array | Matrix | null} x
 *            Initial value
 * @param  {Number | BigNumber | Boolean | Complex | Unit | Array | Matrix | null} y
 *            Value to subtract from `x`
 * @return {Number | BigNumber | Complex | Unit | Array | Matrix}
 *            Subtraction of `x` and `y`
 */
module.exports = function subtract(x, y) {
  if (arguments.length != 2) {
    throw new TypeError('Too ' + (arguments.length > 2 ? 'many' : 'few') +
    ' arguments (expected: 2, actual: ' + arguments.length + ')');
  }

  if (isNumber(x)) {
    if (isNumber(y)) {
      // number - number
      return x - y;
    }
    else if (isComplex(y)) {
      // number - complex
      return new Complex (
          x - y.re,
          - y.im
      );
    }
  }
  else if (isComplex(x)) {
    if (isNumber(y)) {
      // complex - number
      return new Complex (
          x.re - y,
          x.im
      )
    }
    else if (isComplex(y)) {
      // complex - complex
      return new Complex (
          x.re - y.re,
          x.im - y.im
      )
    }
  }

  if (x instanceof BigNumber) {
    // try to convert to big number
    if (isNumber(y)) {
      y = toBigNumber(y, x.constructor);
    }
    else if (isBoolean(y) || y === null) {
      y = new x.constructor(y ? 1 : 0);
    }

    if (y instanceof BigNumber) {
      return x.minus(y);
    }

    // downgrade to Number
    return subtract(x.toNumber(), y);
  }
  if (y instanceof BigNumber) {
    // try to convert to big number
    if (isNumber(x)) {
      x = toBigNumber(x, y.constructor);
    }
    else if (isBoolean(x) || x === null) {
      x = new y.constructor(x ? 1 : 0);
    }

    if (x instanceof BigNumber) {
      return x.minus(y)
    }

    // downgrade to Number
    return subtract(x, y.toNumber());
  }

  if (isUnit(x)) {
    if (isUnit(y)) {
      if (x.value == null) {
        throw new Error('Parameter x contains a unit with undefined value');
      }

      if (y.value == null) {
        throw new Error('Parameter y contains a unit with undefined value');
      }

      if (!x.equalBase(y)) {
        throw new Error('Units do not match');
      }

      var res = x.clone();
      res.value -= y.value;
      res.fixPrefix = false;

      return res;
    }
  }

  if (isCollection(x) || isCollection(y)) {
    return collection.deepMap2(x, y, subtract);
  }

  if (isBoolean(x) || x === null) {
    return subtract(+x, y);
  }
  if (isBoolean(y) || y === null) {
    return subtract(x, +y);
  }

  throw new TypeError('Unexpected type of argument in function add'); // TODO better error
};