function groupBySeries (coll, iteratee, callback) {
        return groupByLimit$1(coll, 1, iteratee, callback)
    }
The same as [`groupBy`]{@link module:Collections.groupBy} but runs only a single async operation at a time.

@name groupBySeries
@static
@memberOf module:Collections
@method
@see [async.groupBy]{@link module:Collections.groupBy}
@category Collection
@param {Array|Iterable|AsyncIterable|Object} coll - A collection to iterate over.
@param {AsyncFunction} iteratee - An async function to apply to each item in
`coll`.
The iteratee should complete with a `key` to group the value under.
Invoked with (value, callback).
@param {Function} [callback] - A callback which is called when all `iteratee`
functions have finished, or an error occurs. Result is an `Object` whose
properties are arrays of values which returned the corresponding key.
@returns {Promise} a promise, if no callback is passed