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LINQ - Extension methods and Func<T,TResult>

I have the following code which works fine

Func<ManagementInfoListData.ManagementInfoListRow, String> groupingFunction = GroupData;

        public static String GroupData(ManagementInfoListData.ManagementInfoListRow dataRow)
        {
            String[] columnNames = new[] {"QuestionTypeCv"};
            stringBuilder.Remove(0, stringBuilder.Length);
            // we always group on month of the transferDate
            stringBuilder.Append(((DateTime)dataRow["TransferDate"]).Month);


            foreach (String column in columnNames)
            {
                stringBuilder.Append(",");
                stringBuilder.Append(dataRow[column].ToString());
            }

            return stringBuilder.ToString();
        }

var groupedDataRow = managementInfoListDataTable.AsQueryable().GroupBy(groupingFunction);

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Now I would like to change it so that I can pass the columnNames instead that it's in the groupData-Function

Something like

public static String GroupData(ManagementInfoListData.ManagementInfoListRow dataRow, String[] columnNames )
{
stringBuilder.Remove(0, stringBuilder.Length);
// we always group on month of the transferDate
stringBuilder.Append(((DateTime)dataRow["TransferDate"]).Month);

foreach (String column in columnNames)
{
stringBuilder.Append(",");
stringBuilder.Append(dataRow[column].ToString());
}

return stringBuilder.ToString();
}

kaufmed

OK, so what am I missing? It seems as though you simply want to add a parameter to your method (which it looks like you've already worked out). Does that code not work?

Dirk Haest

ASKER

The adaptation to the method is no issue. See below.
But how do I need to call it ?
Func<ManagementInfoListData.ManagementInfoListRow, String[], String> groupingFunctionTwo = GroupDataTwo;

var groupedDataRowTwo = managementInfoListDataTable.AsQueryable().GroupBy(groupingFunctionTwo);

If so, I get an error: the type arguments cannot be infered ...

public static String GroupDataTwo(ManagementInfoListData.ManagementInfoListRow dataRow, String[] columnNames)
{
stringBuilder.Remove(0, stringBuilder.Length);
// we always group on month of the transferDate
stringBuilder.Append(((DateTime)dataRow["TransferDate"]).Month);

foreach (String column in columnNames)
{
stringBuilder.Append(",");
stringBuilder.Append(dataRow[column].ToString());
}

return stringBuilder.ToString();
}

kaufmed

This is because the GroupBy method expects a function that takes in a ManagementInfoListRow and returns a String (the key). In other words, the function you pass to GroupBy should be:

Func<ManagementInfoListRow, String> fun;

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I'll have to think about how to achieve your desired goal.

Dirk Haest

ASKER

I agree with your conclusion above, but what I want is to use the groupBy method (which works as I want), but instead of hardcoding the fieldnames in the GroupData-function, I want to pass it to the function.

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Dirk Haest

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Dirk Haest

ASKER

Implemented this solution which works very well

LINQ - Extension methods and Func&lt;T,TResult&gt;

LINQ - Extension methods and Func<T,TResult>