/// <summary> /// Groups the projected elements of an option by a selected key. /// </summary> /// <typeparam name="TSource">The type of the elements of <paramref name="source"/>.</typeparam> /// <typeparam name="TKey">The type of the key used to group elements.</typeparam> /// <typeparam name="TElement"> /// The type of the transformed elements to include in the grouping. /// </typeparam> /// <param name="source">A source option.</param> /// <param name="keySelector"> /// A function to select the key that corresponds to an element of <paramref name="source"/>. /// </param> /// <param name="elementSelector"> /// A function to transform an element of <paramref name="source"/> to an element to include /// in a grouping. /// </param> /// <returns> /// An option that contains a grouping for the projected element of <paramref /// name="source"/>, if <paramref name="source"/> is full; otherwise, an empty option. /// </returns> /// <exception cref="ArgumentNullException"> /// <paramref name="source"/>, <paramref name="keySelector"/>, or <paramref /// name="elementSelector"/> is <see langword="null"/>. /// </exception> public static IOpt <IOptGrouping <TKey, TElement> > GroupBy <TSource, TKey, TElement>(this IOpt <TSource> source, Func <TSource, TKey> keySelector, Func <TSource, TElement> elementSelector) => source.GroupBy(keySelector, elementSelector, null);
/// <summary> /// Groups the projected elements of an option by a selected key. /// </summary> /// <typeparam name="TSource">The type of the elements of <paramref name="source"/>.</typeparam> /// <typeparam name="TKey">The type of the key used to group elements.</typeparam> /// <typeparam name="TElement"> /// The type of the transformed elements to include in the grouping. /// </typeparam> /// <param name="source">A source option.</param> /// <param name="keySelector"> /// A function to select the key that corresponds to an element of <paramref name="source"/>. /// </param> /// <param name="elementSelector"> /// A function to transform an element of <paramref name="source"/> to an element to include /// in a grouping. /// </param> /// <param name="comparer"> /// A comparer to determine whether keys are equal. (This parameter is ignored.) /// </param> /// <returns> /// An option that contains a grouping for the projected element of <paramref /// name="source"/>, if <paramref name="source"/> is full; otherwise, an empty option. /// </returns> /// <exception cref="ArgumentNullException"> /// <paramref name="source"/>, <paramref name="keySelector"/>, or <paramref /// name="elementSelector"/> is <see langword="null"/>. /// </exception> public static IOpt <IOptGrouping <TKey, TElement> > GroupBy <TSource, TKey, TElement>(this IOpt <TSource> source, Func <TSource, TKey> keySelector, Func <TSource, TElement> elementSelector, IEqualityComparer <TKey> comparer) => source.GroupBy(keySelector, elementSelector, GetGrouping);
/// <summary> /// Groups the projected elements of an option by a selected key, then applies a transform to /// each grouping. /// </summary> /// <typeparam name="TSource">The type of the elements of <paramref name="source"/>.</typeparam> /// <typeparam name="TKey">The type of the key used to group elements.</typeparam> /// <typeparam name="TElement"> /// The type of the transformed elements to include in the grouping. /// </typeparam> /// <typeparam name="TResult">The type of the result value for each grouping.</typeparam> /// <param name="source">A source option.</param> /// <param name="keySelector"> /// A function to select the key that corresponds to an element of <paramref name="source"/>. /// </param> /// <param name="elementSelector"> /// A function to transform an element of <paramref name="source"/> to an element to include /// in a grouping. /// </param> /// <param name="resultSelector">A function to select a result value for each grouping.</param> /// <returns> /// An option that contains the result of applying <paramref name="resultSelector"/> to the /// grouping for the projected element of <paramref name="source"/>, if <paramref /// name="source"/> is full; otherwise, an empty option. /// </returns> /// <exception cref="ArgumentNullException"> /// <paramref name="source"/>, <paramref name="keySelector"/>, <paramref /// name="elementSelector"/>, or <paramref name="resultSelector"/> is <see langword="null"/>. /// </exception> public static IOpt <TResult> GroupBy <TSource, TKey, TElement, TResult>(this IOpt <TSource> source, Func <TSource, TKey> keySelector, Func <TSource, TElement> elementSelector, Func <TKey, IOpt <TElement>, TResult> resultSelector) => source.GroupBy(keySelector, elementSelector, resultSelector, null);
