ascending descending in LINQ - can one change the order via parameter

Question

I have a method which is given the parameter  bool sortAscending   Now I want to use LINQ to create sorted list depending on this parameter  I got then this   var ascendingQuery   from data in dataList                       orderby data Property ascending                       select data   var descendingQuery   from data in dataList                       orderby data Property descending                       select data    As you can see  both queries differ only in  ascending  resp   descending   I d like to merge both queries  but I don t know how  Does anyone have the answer

User · Accepted Answer

You can easily create your own extension method on IEnumerable or IQueryable:

public static IOrderedEnumerable<TSource> OrderByWithDirection<TSource,TKey>
    (this IEnumerable<TSource> source,
     Func<TSource, TKey> keySelector,
     bool descending)
{
    return descending ? source.OrderByDescending(keySelector)
                      : source.OrderBy(keySelector);
}

public static IOrderedQueryable<TSource> OrderByWithDirection<TSource,TKey>
    (this IQueryable<TSource> source,
     Expression<Func<TSource, TKey>> keySelector,
     bool descending)
{
    return descending ? source.OrderByDescending(keySelector)
                      : source.OrderBy(keySelector);
}

Yes, you lose the ability to use a query expression here - but frankly I don't think you're actually benefiting from a query expression anyway in this case. Query expressions are great for complex things, but if you're only doing a single operation it's simpler to just put that one operation:

var query = dataList.OrderByWithDirection(x => x.Property, direction);

User · Answer

What about ordering desc by the desired property      blah   blah OrderByDescending x   gt  x Property     And then doing something like    if   descending             blah   blah Reverse         else              Already sorted desc          Is it Reverse   too slow

User · Answer

In addition to the beautiful solution given by  Jon Skeet  I also needed ThenBy and ThenByDescending  so I am adding it based on his solution       public static IOrderedEnumerable lt TSource gt  ThenByWithDirection lt TSource  TKey gt            this IOrderedEnumerable lt TSource gt  source            Func lt TSource  TKey gt  keySelector             bool descending                return descending                   source ThenByDescending keySelector                   source ThenBy keySelector

User · Answer

In terms of how this is implemented  this changes the method - from OrderBy ThenBy to OrderByDescending ThenByDescending  However  you can apply the sort separately to the main query     var qry   from         or just dataList AsEnumerable   AsQueryable    if sortAscending        qry   qry OrderBy x  gt x Property     else       qry   qry OrderByDescending x  gt x Property       Any use  You can create the entire  order  dynamically  but it is more involved     Another trick  mainly appropriate to LINQ-to-Objects  is to use a multiplier  of -1 1  This is only really useful for numeric data  but is a cheeky way of achieving the same outcome

User · Answer

What about ordering desc by the desired property      blah   blah OrderByDescending x   gt  x Property     And then doing something like    if   descending             blah   blah Reverse         else              Already sorted desc          Is it Reverse   too slow

User · Answer

In terms of how this is implemented  this changes the method - from OrderBy ThenBy to OrderByDescending ThenByDescending  However  you can apply the sort separately to the main query     var qry   from         or just dataList AsEnumerable   AsQueryable    if sortAscending        qry   qry OrderBy x  gt x Property     else       qry   qry OrderByDescending x  gt x Property       Any use  You can create the entire  order  dynamically  but it is more involved     Another trick  mainly appropriate to LINQ-to-Objects  is to use a multiplier  of -1 1  This is only really useful for numeric data  but is a cheeky way of achieving the same outcome

User · Answer

In terms of how this is implemented  this changes the method - from OrderBy ThenBy to OrderByDescending ThenByDescending  However  you can apply the sort separately to the main query     var qry   from         or just dataList AsEnumerable   AsQueryable    if sortAscending        qry   qry OrderBy x  gt x Property     else       qry   qry OrderByDescending x  gt x Property       Any use  You can create the entire  order  dynamically  but it is more involved     Another trick  mainly appropriate to LINQ-to-Objects  is to use a multiplier  of -1 1  This is only really useful for numeric data  but is a cheeky way of achieving the same outcome

User · Answer

In addition to the beautiful solution given by  Jon Skeet  I also needed ThenBy and ThenByDescending  so I am adding it based on his solution       public static IOrderedEnumerable lt TSource gt  ThenByWithDirection lt TSource  TKey gt            this IOrderedEnumerable lt TSource gt  source            Func lt TSource  TKey gt  keySelector             bool descending                return descending                   source ThenByDescending keySelector                   source ThenBy keySelector

User · Answer

In terms of how this is implemented  this changes the method - from OrderBy ThenBy to OrderByDescending ThenByDescending  However  you can apply the sort separately to the main query     var qry   from         or just dataList AsEnumerable   AsQueryable    if sortAscending        qry   qry OrderBy x  gt x Property     else       qry   qry OrderByDescending x  gt x Property       Any use  You can create the entire  order  dynamically  but it is more involved     Another trick  mainly appropriate to LINQ-to-Objects  is to use a multiplier  of -1 1  This is only really useful for numeric data  but is a cheeky way of achieving the same outcome

[c#] ascending/descending in LINQ - can one change the order via parameter?

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