Sort one list by another

Another LINQ-approach:

 var orderedByIDList = from i in ids 
                       join o in objectsWithIDs
                       on i equals o.ID
                       select o;

One way of doing it:

List<int>  order = ....;
List<Item> items = ....;

Dictionary<int,Item> d = items.ToDictionary(x => x.ID);

List<Item> ordered = order.Select(i => d[i]).ToList();

Not an answer to this exact question, but if you have two arrays, there is an overload of Array.Sort that takes the array to sort, and an array to use as the 'key'

https://msdn.microsoft.com/en-us/library/85y6y2d3.aspx

Array.Sort Method (Array, Array)
Sorts a pair of one-dimensional Array objects (one contains the keys and the other contains the corresponding items) based on the keys in the first Array using the IComparable implementation of each key.

Join is the best candidate if you want to match on the exact integer (if no match is found you get an empty sequence). If you want to merely get the sort order of the other list (and provided the number of elements in both lists are equal), you can use Zip.

var result = objects.Zip(ints, (o, i) => new { o, i})
                    .OrderBy(x => x.i)
                    .Select(x => x.o);

Pretty readable.

Here is an extension method which encapsulates Simon D.'s response for lists of any type.

public static IEnumerable<TResult> SortBy<TResult, TKey>(this IEnumerable<TResult> sortItems,
                                                         IEnumerable<TKey> sortKeys,
                                                         Func<TResult, TKey> matchFunc)
{
    return sortKeys.Join(sortItems,
                         k => k,
                         matchFunc,
                         (k, i) => i);
}

Usage is something like:

var sorted = toSort.SortBy(sortKeys, i => i.Key);