reduce.js 2.4 KB

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  1. import _curry3 from "./internal/_curry3.js";
  2. import _xReduce from "./internal/_xReduce.js";
  3. import _xwrap from "./internal/_xwrap.js";
  4. /**
  5. * Returns a single item by iterating through the list, successively calling
  6. * the iterator function and passing it an accumulator value and the current
  7. * value from the array, and then passing the result to the next call.
  8. *
  9. * The iterator function receives two values: *(acc, value)*. It may use
  10. * [`R.reduced`](#reduced) to shortcut the iteration.
  11. *
  12. * The arguments' order of [`reduceRight`](#reduceRight)'s iterator function
  13. * is *(value, acc)*.
  14. *
  15. * Note: `R.reduce` does not skip deleted or unassigned indices (sparse
  16. * arrays), unlike the native `Array.prototype.reduce` method. For more details
  17. * on this behavior, see:
  18. * https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Array/reduce#Description
  19. *
  20. * Be cautious of mutating and returning the accumulator. If you reuse it across
  21. * invocations, it will continue to accumulate onto the same value. The general
  22. * recommendation is to always return a new value. If you can't do so for
  23. * performance reasons, then be sure to reinitialize the accumulator on each
  24. * invocation.
  25. *
  26. * Dispatches to the `reduce` method of the third argument, if present. When
  27. * doing so, it is up to the user to handle the [`R.reduced`](#reduced)
  28. * shortcuting, as this is not implemented by `reduce`.
  29. *
  30. * @func
  31. * @memberOf R
  32. * @since v0.1.0
  33. * @category List
  34. * @sig ((a, b) -> a) -> a -> [b] -> a
  35. * @param {Function} fn The iterator function. Receives two values, the accumulator and the
  36. * current element from the array.
  37. * @param {*} acc The accumulator value.
  38. * @param {Array} list The list to iterate over.
  39. * @return {*} The final, accumulated value.
  40. * @see R.reduced, R.addIndex, R.reduceRight
  41. * @example
  42. *
  43. * R.reduce(R.subtract, 0, [1, 2, 3, 4]) // => ((((0 - 1) - 2) - 3) - 4) = -10
  44. * // - -10
  45. * // / \ / \
  46. * // - 4 -6 4
  47. * // / \ / \
  48. * // - 3 ==> -3 3
  49. * // / \ / \
  50. * // - 2 -1 2
  51. * // / \ / \
  52. * // 0 1 0 1
  53. *
  54. * @symb R.reduce(f, a, [b, c, d]) = f(f(f(a, b), c), d)
  55. */
  56. var reduce =
  57. /*#__PURE__*/
  58. _curry3(function (xf, acc, list) {
  59. return _xReduce(typeof xf === 'function' ? _xwrap(xf) : xf, acc, list);
  60. });
  61. export default reduce;