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c# - 使用特定列执行“除外”

问题描述

考虑 2 个具有相同架构的表：

var yesterday = new DataTable();
yesterday.Columns.Add("id", typeof(int));
yesterday.Columns.Add("part_number", typeof(string));
yesterday.Columns.Add("description", typeof(string));
yesterday.Columns.Add("comment", typeof(string));
yesterday.Columns.Add("information", typeof(string));
yesterday.Columns.Add("data", typeof(string));
var today = yesterday.Clone();

添加一些数据：

//yesterday data has 3 rows
yesterday.Rows.Add(1, "IVD_002", "IVD_002_RED", "Some comment", "Some information","Some data");
yesterday.Rows.Add(2, "IVD_003", "IVD_003_RED", "Some comment", "Some information", "Some data");
yesterday.Rows.Add(3, "IVD_004", "IVD_004_RED", "Some comment", "Some information", "Some data");

//today's data has the same 3 rows
today.Rows.Add(1, "IVD_002", "IVD_002_RED", "Some comment", "Some information", "Some data");
today.Rows.Add(2, "IVD_003", "IVD_003_RED", "Some comment", "Some information", "Some data");
today.Rows.Add(3, "IVD_004", "IVD_004_RED", "Some comment", "Some information", "Some data");

让我们添加更多数据：

//The New Row:
//In the output table I expect to see only the following row. The "id" column is 5 whereas in previous records there is no row with id = 5, part_number = IVD_002, description = IVD_002_RED
today.Rows.Add(5, "IVD_002", "IVD_002_RED", "Some comment", "Some information", "Some data");

//Another New Row:
//I dont expect to see this row in the result table because we are doing except only on "id","part_number","description" columns
today.Rows.Add(1, "IVD_002", "IVD_002_RED", "ROSES ARE RED", "PEANUTS", "=)");

我的目标是从“今天”表中获取行，但“昨天”表中的行除外，但只比较列“id”、“part_number”、“description”。

真的很感激一个纯 LINQ 解决方案，没有循环。

标签： c#linqdatatableexcept

解决方案

我建议使用!Any. 我更愿意将其转换yesterday DataTable为 a HashSet，这样您就不会不断地线性扫描yesterday匹配项，但我不确定 UiPath 有什么限制。

var result = today.AsEnumerable().Where(t => !yesterday.AsEnumerable().Any(y => (y["id"].Equals(t["id"]) &&
                                                                                 y["part_number"].Equals(t["part_number"]) &&
                                                                                 y["description"].Equals(t["description"]))))
                                 .CopyToDataTable();

如果你可以使用 a HashSet，那么你可以这样做：

var yesterdayHash = yesterday.AsEnumerable().Select(y => new { id = (int)y["id"], partnum = y["part_number"].ToString(), desc = y["description"].ToString() }).ToHashSet();
var result2 = today.AsEnumerable().Where(t => !yesterdayHash.Contains(new { id = (int)t["id"], partnum = t["part_number"].ToString(), desc = t["description"].ToString() })).CopyToDataTable();

Func使用用于创建返回匿名类型的委托的静态类 Cast 助手，您可以创建一个 lambda 变量来保存公共键表达式：

public static class To {
    public static Func<TResult> Func<TResult>(Func<TResult> func) => func;
    public static Func<T, TResult> Func<T, TResult>(Func<T, TResult> func) => func;
}

var selectorFn = To.Func((DataRow r) => new { id = r.Field<int>("id"), partnum = r.Field<string>("part_number"), desc = r.Field<string>("description") });
var yesterdayHash2 = yesterday.AsEnumerable().Select(selectorFn).ToHashSet();
var result3 = today.AsEnumerable().Where(t => !yesterdayHash2.Contains(selectorFn(t))).CopyToDataTable();

注意：我更喜欢使用Field<>扩展方法DataRow来获取强类型DataTable列值。

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