/// <summary> /// Groups the data by the values in the given column, and computes aggregate quantities for each group. /// </summary> /// <param name="groupByColumnName">The name of the column to group by.</param> /// <param name="aggregator">A function that computes the aggregate quantities.</param> /// <returns>A new data frame containing the aggregates for each group.</returns> /// <remarks> /// <para>The first column of the returned <see cref="FrameTable"/> has the same name as the /// original <paramref name="groupByColumnName"/> and contains all the distinct /// values of that column in the original view. There is an additional column for each /// dictionary entry returned by <paramref name="aggregator"/>, whose name is the returned /// key and whose values are values returned for each group.</para> /// <para>The function that computes the aggregate receives a <see cref="FrameView"/> containing /// all the rows in the group. To produce aggregate results, it can use values in any of /// the columns. Each invocation of the <paramref name="aggregator"/> must return the same keys /// and values for the same keys must be of the same type. (Values for different keys may be /// of different types.) Aggregate column names are taken from the keys and storage types are /// inferred from the returned values.</para> /// <para>To produce just one aggregate value, you may find it simpler and more efficient /// to use the <see cref="GroupBy(string, Func{FrameView, IReadOnlyDictionary{string, object}})"/> /// overload.</para> /// </remarks> public FrameTable GroupBy(string groupByColumnName, Func <FrameView, IReadOnlyDictionary <string, object> > aggregator) { // Collect rows into groups. int groupByColumnIndex = GetColumnIndex(groupByColumnName); NamedList groupByColumn = columns[groupByColumnIndex]; NullableDictionary <object, List <int> > groups = FindGroups(groupByColumn); // Create a column to hold the group values. NamedList groupsColumn = NamedList.Create(groupByColumnName, groupByColumn.StorageType); // Create an enumerator that feeds the groups into the aggregator and presents them as dictionaries. IEnumerable <IReadOnlyDictionary <string, object> > aggregatesEnumerator = GetGroupEnumerator(groups, aggregator, groupsColumn); // Column-ify and validate the presented dictionaries. List <NamedList> aggregateColumns = DictionaryHelper.ReadDictionaries(aggregatesEnumerator); // Collect the results into a frame table. FrameTable result = new FrameTable(); // First column is the group values. result.AddColumn(groupsColumn); // Remaining columns are aggregate columns. foreach (NamedList aggregateColumn in aggregateColumns) { result.AddColumn(aggregateColumn); } return(result); }
/// <summary> /// Constructs a new frame table from a sequence of dictionaries. /// </summary> /// <param name="dictionaries">A enumerable set of dictionaries, one for each row, whose /// keys are the column names and whose values are the cell value of the column for that row.</param> /// <returns>A new frame table with data from the dictionaries.</returns> /// <remarks><para>The storage type of each column is inferred from the types of objects /// encountered are the frame table is constructed.</para></remarks> public static FrameTable FromDictionaries(IEnumerable <IReadOnlyDictionary <string, object> > dictionaries) { if (dictionaries == null) { throw new ArgumentNullException(nameof(dictionaries)); } List <NamedList> columns = DictionaryHelper.ReadDictionaries(dictionaries); // Collect the results into a frame table. FrameTable result = new FrameTable(columns); return(result); }