LINQ group by property as a parameter

Question

I have a list of objects that I want to query using LINQ. I want to be able to group them by a property.

var query = from item in expense
    orderby item.ExpenseTime descending
    group item by item.Location;

var query = from item in expense
    orderby item.ExpenseTime descending
    group item by item.ExpenseType;

var query = from item in expense
    orderby item.ExpenseTime descending
    group item by item.Person;

Is there a way to specify the property as an argument of a method?

public static void GetExpensesBy(List<Expense> expense, Property myGroupingProperty)
{
    var query = from item in expense
                orderby item.ExpenseTime descending
                group item by item.myGroupingProperty;

    // ....
}

Note that after the query there is code that is generic and does not care about the group.

score 9 · Accepted Answer · answered May 04 '12 at 09:03

9

If you modify your GetExpenseBy as below

public static void GetExpensesBy<TKey>(List<Expense> expense, 
                                       Func<Expense, TKey> myGroupingProperty)
{
    var query = (from item in expense
                 orderby item.ExpenseTime descending
                 select item).GroupBy(myGroupingProperty);
    // ....
}

Then you can call this function as

GetExpensesBy(expense, item => item.Location);
GetExpensesBy(expense, item => item.Person);
GetExpensesBy(expense, item => item.ExpenseType);

answered May 04 '12 at 09:03

Ramesh

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Could i make a multi GroupBy in the same expression? example: group by location, then person in the same expression? like GetExpensesBy(expense, item => item.Location, item => item.Person); – Marcel James Aug 21 '13 at 14:02
1

If you need to groupby both person and location you can use `GetExpensesBy(expense, item => new { item.Location, item.Person});` – Ramesh Aug 22 '13 at 03:04
how convert it to Dictionary> – Alex David Feb 27 '14 at 06:44
What is the TKey going to contain? – Ramesh Feb 27 '14 at 08:45
How do you get the newly created collection from the function as the function is a void that returns nothing? – Rani Radcliff Mar 22 '18 at 15:38
@RaniRadcliff - I used void as the OP had it void in their question. – Ramesh Mar 24 '18 at 18:27

score 0 · Answer 2 · answered May 04 '12 at 08:58

Microsoft wrote a Dynamic Linq library.

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

http://msdn2.microsoft.com/en-us/vcsharp/bb894665.aspx

This lib will allow you to specify any of the Linq query dyanamically

daryal · Answer 3 · 2012-05-04T09:07:53.187

0

public static void GetExpensesBy<T>(List<Expense> expense, Expression<Func<A,T>> groupbyExpression)
{
    var query = from item in expense
                orderby item.ExpenseTime descending;
    query.GroupBy(groupbyExpression);

    // ....
}

and create the expression like;

Expression<Func<Expense, string>> group = (q) => q.Location;

edited May 04 '12 at 09:07

answered May 04 '12 at 09:02

daryal

14,643
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why you want to use Expression>? – Ramesh May 04 '12 at 09:11

LINQ group by property as a parameter

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