Question
I currently have a piece of code that takes a DataView, selects the values of a single column, groups by those values, then outputs the count (to get a histogram, of sorts):
string columnName;
var dataSource = grid.DataSource as System.Data.DataView;
var values = dataSource.OfType<System.Data.DataRowView>()
.Select(r => r[columnName]);
_GroupedRowCounts = values.GroupBy(r => r[columnName])
.ToDictionary(v => v.Key, v => v.Count());
That works fine, but turns out I need to group by an arbitrary number of columns that I don't know at compile time.
I assume I can use System.Linq.Dynamic for this, but I've found its documentation rather lacking (starting from: which of the GitHub projects is current?). I can apparently use DynamicExpression.CreateClass() to dynamically create a class with properties based on the columns I want to group by, something like:
List<DataColumn> columns;
Type dynamicDataClass = DynamicExpression.CreateClass(columns.Select(c => new DynamicProperty(c.ColumnName, c.DataType)));
However, I'm unclear about:
- how do I then pass this class to a
SelectandGroupBycall? System.Linq.Dynamic exposes a Select() overload that takes a string — do I just pass the class's property names? How does System.Linq.Dynamic know to use the dynamically generated type? - how do I fill this with values? I know I can use Activator to do so manually, but is there a built-in way of mapping this to the values of the original objects, or do I need to custom-roll this?
- am I even on the right track at all? The examples don't seem to use DynamicExpression, etc., but rather just strings.
Popular Answer
This answer is for if you would like to get around using an external library. This is going to be a little bit more inefficient than using a library. It seems that there is also another library that you can try called Linq.Dynamic.Core. It seems a little more robust.
I would convert the result of your linq query to a list of type Dictionary. Using the top answer from this post: LINQ query to return a Dictionary<string, string>
Then you can sort doing something like this:
List<Dictionary<string, string>> list = new List<Dictionary<string, string>>();
list.OrderBy(x => x["columnName"]).ToList();