C# in Depth

368 APPENDIX LINQ standard query operatorsTable A.11Quantifier examplesExpressionwords.All(word => word.Length > 3)words.All(word => word.Length > 2)words.Any()words.Any(word => word.Length == 6)words.Any(word => word.Length == 5)words.Contains("FOUR")words.Contains("FOUR",StringComparer.OrdinalIgnoreCase)Resultfalse ("one" and "two" have exactly threeletters)Truetrue (the sequence is not empty)false (no six-letter words)true ("three" satisfies the condition)FalseTrueA.12 FilteringThe two filtering operators are OfType and Where. For details and examples of theOfType operator, see the conversion operators section (A.3). The Where operator (seetable A.12) has overloads so that the filter can take account of the element’s index. It’sunusual to require the index, and the where clause in query expressions doesn’t usethis overload. Where always uses deferred execution.Table A.12Filtering examplesExpressionwords.Where(word => word.Length > 3)words.Where((word, index) =>index < word.Length)Result"zero", "three", "four""zero", // length=4, index=0"one", // length=3, index=1"two", // length=3, index=2"three", // length=5, index=3// Not "four", length=4, index=4A.13 Set-based operationsIt’s natural to be able to consider two sequences as sets of elements. The four setbasedoperators all have two overloads, one using the default equality comparison forthe element type, and one where the comparison is specified in an extra parameter.All of them use deferred execution.The Distinct operator is the simplest—it acts on a single sequence, and just returnsa new sequence of all the distinct elements, discarding duplicates. The other operatorsalso make sure they only return distinct values, but they act on two sequences:■■■Intersect returns elements that appear in both sequences.Union returns the elements that are in either sequence.Except returns the elements that are in the first sequence but not in the second.(Elements that are in the second sequence but not the first are not returned.)Licensed to Rhona Hadida