Using linq with if-query

Question

i have the following code which groups a list of FileInfos:

            var group_infos =
            from info in fileInfos
            where info.Length < 1024 * 1024
            group info by info.Name into g
            where g.Count() > 1
            orderby g.Count() descending, g.Key
            select g;

Now i want to do an if-query on the group-clausel. Maybe with help of a string

string groupClausel = "Name";

or enum:

    public enum FilterMethod
    {
        Directory,
        CreationTime,
        DirectoryName,
        Extension,
        Length, 
        Name
    }

But i dont know how to check the string or enum in group-clausel.. I know there s a syntax like

    group info by (groupClausel == "Extension" ? info.Extension : info.Name) into g

But this let me just select on two attributes...

Do you people have an idea?

No, i want to check which group-method the user wants.. If he wants to group by name: group by name. If he wants to group by length: group by length. if he wants to group by....... — Basssprosse, Jan 08 '17 at 18:10

score 1 · Accepted Answer · answered Jan 08 '17 at 18:12

You could use method syntax instead of query syntax here, it will be more maintainable and readable in my oppinion.

For example, you could make a method which returns group by key selector function:

private Func<FileInfo, object> GetGroupByKeySelector(FilterMethod filterMethod)
{
    Func<FileInfo, object> keySelector = null;
    switch (filterMethod)
    {
        case FilterMethod.Directory:
            keySelector = f => f.Directory;
            break;

        case FilterMethod.CreationTime:
            keySelector = f => f.CreationTime;
            break;

        case FilterMethod.DirectoryName:
            keySelector = f => f.DirectoryName;
            break;

        case FilterMethod.Extension:
            keySelector = f => f.Extension;
            break;

        case FilterMethod.Length:
            keySelector = f => f.Extension;
            break;

        default:
            keySelector = f => f.Name;
            break;
    }
    return keySelector;
}

And then you can use it as described below:

FilterMethod prop = FilterMethod.CreationTime;
var groupInfos = fileInfos
    .Where(f => f.Length < 1024 * 1024)
    .GroupBy(GetGroupByKeySelector(prop))
    .Where(g => g.Count() > 1)
    .OrderByDescending(g => g.Count())
    .OrderBy(g => g.Key)
    .Select(g => g);

Additionaly, you can use System.Net.Reflection library to avoid switch-case inside GetGroupByKeySelector method if your enum reflects FileInfo property names.

Using linq with if-query

1 Answers1