Sort List based on Array

Question

I am trying to sort a custom list based on a string array, but I am failing miserably e.g. its not sorting the list at all,

Public class CrateOrder
{
   public int Id { get; set; }
   public string Name { get; set; }
   public Stream OrderStream { get; set; }
}

string[] selectedFruits = {"Apple", "Mango"};  // in real get from web services
var selectedFruitsList = selectedFruits.ToList();

List<CrateOrder> cFruit = GetCrateOrderFromWebServices();

var sorted = cFruit.OrderBy(s => selectedFruitsList.IndexOf(s.Name)).ToList();

It's not sorting the list properly, I want CrateOrder list item to be ordered based on selectedFruits...

I still don't understand how you are trying to sort your cFruit with your selectedFruits. An input and expected output for cFruit would help. — ryanyuyu
– ryanyuyu, Commented Feb 12, 2015 at 14:18
This looks fine to me - maybe I'm just missing the same thing, but are you sure your cFruit list items actually have Name properties that match your selectedFruits? — Dana Cartwright
– Dana Cartwright, Commented Feb 12, 2015 at 14:20
That's not a duplicate, there's something else going on here. — Sergey Kalinichenko
– Sergey Kalinichenko, Commented Feb 12, 2015 at 14:21
I suspect this is a case-sensitivity issue, IndexOf will do a case-sensitive search by default, unless specifying a different rule. — Jamiec
– Jamiec, Commented Feb 12, 2015 at 14:22

Jamiec · Accepted Answer · 2015-02-12 14:37:13Z

2

If the Name property of your fruit does not match your ordering list exactly, IndexOf will always return -1. To get around this specify a case-insensitive StringComparison, but that is not available as an overload to IndexOf so you have to use a slightly more complex method:

var sorted = cFruit.OrderBy(
                     s => selectedFruitsList.FindIndex(
                            x => x.Equals(s.Name, StringComparison.OrdinalIgnoreCase)) )
                  .ToList();

edited Feb 12, 2015 at 14:37

answered Feb 12, 2015 at 14:25

Jamiec

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4 Comments

Mathematics Over a year ago

it worked with some adjustments, e.g. OrderByDescending and converting s.Name tolower, i know it shouldn't matter but thats how it worked, thanks

Jamiec Over a year ago

The StringComparison.OrdinalIgnoreCase was specifically to not have to do any case conversion.

Mathematics Over a year ago

I know, but for some reason, it wasn't working for me, I will look into it later, too occupied at this time :(

Jamiec Over a year ago

Here you go: rextester.com/ZOIS35246 - works absolutely fine with no need to change the case of anything (Note the Names have some lowercase starting letters)

Sergey Kalinichenko · Accepted Answer · 2015-02-12 14:22:56Z

2

You are almost there. The code orders the fruit from selectedFruitsList after all other items, because OrderBy order is ascending, and they are the only ones for which a non-negative number is returned.

To fix this, reverse selectedFruits, and negate the result of IndexOf, like this:

string[] selectedFruits = {"Mango", "Apple"};
...
var sorted = cFruit.OrderBy(s => -selectedFruitsList.IndexOf(s.Name)).ToList();

Alternatively, you could expand the code to deal with negative indexes explicitly:

string[] selectedFruits = {"Apple", "Mango"};
...
var sorted = cFruit.OrderBy(s => {
    int index = selectedFruitsList.IndexOf(s.Name);
    return index < 0 ? int.MaxValue : index;
}).ToList();

answered Feb 12, 2015 at 14:22

Sergey Kalinichenko

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Comments

D Stanley · Accepted Answer · 2015-02-12 14:46:21Z

1

I wasn't aware if its case sensitive, can i add ignore culture to it

No - Array.IndexOf does not have parameters that let you customize the equality comparison.

Just change all of your selectedfruits and the search value to lower case:

string[] selectedFruits = {"Apple", "Mango"};  // in real get from web services
var selectedFruitsList = selectedFruits.Select(s => s.ToUpperInvariant()).ToList();

List<CrateOrder> cFruit = GetCrateOrderFromWebServices();

var sorted = cFruit.OrderBy(s => selectedFruitsList.IndexOf(s.Name.ToUpperInvariant())).ToList;

edited Feb 12, 2015 at 14:46

answered Feb 12, 2015 at 14:27

D Stanley

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2 Comments

Jamiec Over a year ago

You should at very least be using ToLowerInvariant, but the recommendation is "Use the String.ToUpperInvariant method instead of the String.ToLowerInvariant method when you normalize strings for comparison"

D Stanley Over a year ago

@Jamiec fair enough - modified.

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