C# in Depth

366 APPENDIX LINQ standard query operatorssequence. Both use deferred execution, and stream the left sequence but buffer theright sequence.Table A.8Join examplesExpressionnames.Join // Left sequence(colors, // Right sequencename => name[0], // Left key selectorcolor => color[0], // Right key selector// Projection for result pairs(name, color) => name+" - "+color)names.GroupJoin(colors,name => name[0],color => color[0],// Projection for key/sequence pairs(name, matches) => name+": "+string.Join("/", matches.ToArray()))Result"Robin - Red","Ruth - Red","Bob - Blue","Bob - Beige""Robin: Red","Ruth: Red","Bob: Blue/Beige","Emma: "For the join examples in table A.8, we’ll match a sequence of names (Robin, Ruth,Bob, Emma) against a sequence of colors (Red, Blue, Beige, Green) by looking at thefirst character of both the name and the color, so Robin will join with Red and Bobwill join with both Blue and Beige, for example.Note that Emma doesn’t match any of the colors—the name doesn’t appear at allin the results of the first example, but it does appear in the second, with an emptysequence of colors.A.9 PartitioningThe partitioning operators either skip an initial part of the sequence, returning only therest, or take only the initial part of a sequence, ignoring the rest. In each case you caneither specify how many elements are in the first part of the sequence, or specify a condition—thefirst part of the sequence continues until the condition fails. After the conditionfails for the first time, it isn’t tested again—it doesn’t matter whether laterelements in the sequence match or not. All of the partitioning operators (see table A.9)use deferred execution.Table A.9Partitioning examplesExpressionResultwords.Take(3)words.Skip(3)"zero", "one", "two""three", "four"Licensed to Rhona Hadida