Function _getSubstring

src/function/matrix/subset.js:142–173

* Retrieve a subset of a string * @param {string} str string from which to get a substring * @param {Index} index An index or list of indices (character positions) * @returns {string} substring * @private

(str, index)

 * @private
 */
function _getSubstring (str, index) {
  if (!isIndex(index)) {
    // TODO: better error message
    throw new TypeError('Index expected')
  }

  if (isEmptyIndex(index)) { return '' }
  validateIndexSourceSize(Array.from(str), index)

  if (index.size().length !== 1) {
    throw new DimensionError(index.size().length, 1)
  }

  // validate whether the range is out of range
  const strLen = str.length
  validateIndex(index.min()[0], strLen)
  validateIndex(index.max()[0], strLen)

  const range = index.dimension(0)

  let substr = ''
  function callback (v) {
    substr += str.charAt(v)
  }
  if (Number.isInteger(range)) {
    callback(range)
  } else {
    range.forEach(callback)
  }

  return substr
}

/**
 * Replace a substring in a string