How to build group-by dynamically on a list of dictionaries

问题

I am trying to perform a groupby on an IEnumerable. The problem is that I do not know at compile-time which fields i want to groupby. I have found another post on stack that explains how to do this when the class is known and has properties, but in my case i am dealing with a dictionary and the keys are also only known at run-time.

My code would resemble something like this (i know this doesn't compile...):

private object GetValuesGroupedBy(List<string> groupbyNames, List<string> summableNames)
{
     // get the list of items in the grid
     var listOfDicos = grid.AllItems;

     return listOfDicos
                .GroupBy(x => new { x[groupbyNames[0]], 
                                    x[groupbyNames[1]], 
                                    x[groupbyNames[2]] })
                .Select(group => new { group.Key, 
                                       group.Sum(x => x[summableNames[0]]), 
                                       group.Sum(x => x[summableNames[1]]) });
}

Any ideas? I've started looking into Dynamic LINQ but am stuck (because I am not using properties but a Key/Value collection)...

Thanks everybody!!

Sean

回答1:

This will help you: http://weblogs.asp.net/scottgu/archive/2008/01/07/dynamic-linq-part-1-using-the-linq-dynamic-query-library.aspx

And this: Dynamic LINQ OrderBy on IEnumerable<T>

回答2:

So I am able to get the groupby to work... (the select statement is another question). Thanks to c0d1ng for putting me on the right path. The syntax was not so trivial because I am using indexers and not properties...

Below is my code:

    private void GetValuesGroupedBy(List<Dictionary<string, object>> list, List<string> groupbyNames, List<string> summableNames)
    {
        // build the groupby string
        StringBuilder groupBySB = new StringBuilder();
        groupBySB.Append("new ( ");
        bool useComma = false;
        foreach (var name in groupbyNames)
        {
            if (useComma)
                groupBySB.Append(", ");
            else
                useComma = true;

            groupBySB.Append("it[\"");
            groupBySB.Append(name);
            groupBySB.Append("\"]");
            groupBySB.Append(" as ");
            groupBySB.Append(name);
        }
        groupBySB.Append(" )");

        var groupby = list.GroupBy(groupBySB.ToString(), "it");
    }

来源：https://stackoverflow.com/questions/10797997/how-to-build-group-by-dynamically-on-a-list-of-dictionaries

标签

linq

dynamic

datatable

group-by