Sort a list in C# by custom index and sameness

Question

I have some large files (5000+ line items) with brief information of hardware parts.

Put simply, each part has an Id and name, and all parts from a file are added to a List collection, like:

void Main() { var parts = new List<dynamic>(); parts.Add(make(1, "Part A")); parts.Add(make(2, "Part B")); parts.Add(make(3, "Part C")); parts.Add(make(4, "Part D")); parts.Add(make(5, "Part A")); parts.Add(make(6, "Part E")); parts.Add(make(7, "Part B")); parts.Add(make(8, "Part F")); parts.Add(make(9, "Part G")); parts.Add(make(10, "Part B")); } dynamic make(int id, string name) { dynamic o = new ExpandoObject(); o.id = id; o.name = name; return o; }

This list of parts is sorted, first by a custom sorting order of part Ids (determined separately) available as a List of Ids:

var customOrderPartIds = new List<int>() { 10, 8, 6, 4, 2, 9, 7, 5, 3, 1 }; parts.OrderBy(p => customOrderPartIds.IndexOf(p.id)).ToList();

/* This gives the needed order: 10 - Part B 8 - Part F 6 - Part E 4 - Part D 2 - Part B 9 - Part G 7 - Part B 5 - Part A 3 - Part C 1 - Part A */

Now, the second ordering I need is for same part names to be together, but keeping the first ordering intact, and a part group increment number:

/* This is the needed final order, along with an increment: 10 - Part B - 1 2 - Part B - 1 7 - Part B - 1 8 - Part F - 2 6 - Part E - 3 4 - Part D - 4 9 - Part G - 5 5 - Part A - 6 1 - Part A - 6 3 - Part C - 7 */

How can this be achieved?

Does this answer your question? LINQ OrderBy with more than one field — Connor Stoop
– Connor Stoop, Commented Jun 7, 2021 at 9:55
You can chain ordering by using OrderBy(e => e.Property).ThenBy(e => e.OtherProperty) — Michael Mairegger
– Michael Mairegger, Commented Jun 7, 2021 at 9:59
Thanks. Unfortunately, it doesn't help. If I use ThenBy and do something like parts.OrderBy(p => customOrderPartIds.IndexOf(p.id)).ThenBy(p => p.name).ToList();, the results don't reflect the second ordering as I need it (sample output above). — Nick
– Nick, Commented Jun 7, 2021 at 9:59
Why you use dynamic at all and not a class with a property Id and Name? Even a ValueTuple<int, id> was much better than dynamic. — Tim Schmelter
– Tim Schmelter, Commented Jun 7, 2021 at 10:02
@Nick: don't use dynamic to simplify your questions, that will raise other issues not related to your question then. — Tim Schmelter
– Tim Schmelter, Commented Jun 7, 2021 at 10:04

Wai Ha Lee · Accepted Answer · 2021-06-07 10:28:10Z

2

You could group it, and output again.

var result = parts.OrderBy(p => customOrderPartIds.IndexOf(p.id)) .GroupBy(x => x.name) .SelectMany(x => x);

edited Jun 7, 2021 at 10:28

Wai Ha Lee

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answered Jun 7, 2021 at 10:17

Epic Chen

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1 Comment

Tim Schmelter Over a year ago

Missing the increment number but it's simple to add

Klamsi · Accepted Answer · 2021-06-07 10:33:04Z

Something like that should do as second ordering:

parts = parts.SelectMany( item => parts.First(p => p.Name == item.Name) == item ? parts.Where(p => p.Name == item.Name) : new List<dynamic>()).ToList();

If it is the first one of the group: return all items of the group.

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