C#•2y ago

❔ LINQ distinct from 2 lists preserving order as soon as they are seen

I have 2 lists like this 1: {1, 2, 3} 2: {1, 3, 4} what's the LINQ distinct method for them that provides this output? {1, 2, 3, 4} it should be the functional equivalent as this, and not ordering by value

        List<string> list = new();
        for (int i = 0; i < 50; i++)
        {
            if (!list.Contains(lines[i])) // I know Set exists
                list.Add(lines[i]);
            if (!list.Contains(linesReceived[i]))
                list.Add(linesReceived[i]);
        }

        List<string> list = new();
        for (int i = 0; i < 50; i++)
        {
            if (!list.Contains(lines[i])) // I know Set exists
                list.Add(lines[i]);
            if (!list.Contains(linesReceived[i]))
                list.Add(linesReceived[i]);
        }

50 Replies

MODiX•2y ago

Ero#1111

REPL Result: Success

List<int> list1 = new() { 1, 2, 3 };
List<int> list2 = new() { 1, 3, 4 };
List<int> union = list1.Union(list2).ToList();

union

List<int> list1 = new() { 1, 2, 3 };
List<int> list2 = new() { 1, 3, 4 };
List<int> union = list1.Union(list2).ToList();

union

Result: List<int>

[
  1,
  2,
  3,
  4
]

[
  1,
  2,
  3,
  4
]

Compile: 525.116ms | Execution: 35.438ms | React with ❌ to remove this embed.

Alan72104OP•2y ago

sorry I should've said doing that on a longer list fails

MODiX•2y ago

To compile C# code in Discord, use !eval Example:

!eval for(int i = 0; i < 4; i++) Console.WriteLine(i);

!eval for(int i = 0; i < 4; i++) Console.WriteLine(i);

Please don't try breaking the REPL service. Also, remember to do so in #bot-spam!

MODiX•2y ago

Alan72104#4011

REPL Result: Success

int[] a1 = { 1, 2, 3, 5, 6, 7, 8, 9 };
int[] a2 = { 1, 3, 4, 5, 7, 8, 9, 6 };
int[] names2 = a1.Union(a2).ToArray();
names2

int[] a1 = { 1, 2, 3, 5, 6, 7, 8, 9 };
int[] a2 = { 1, 3, 4, 5, 7, 8, 9, 6 };
int[] names2 = a1.Union(a2).ToArray();
names2

Result: int[]

[
  1,
  2,
  3,
  5,
  6,
  7,
  8,
  9,
  4
]

[
  1,
  2,
  3,
  5,
  6,
  7,
  8,
  9,
  4
]

Compile: 513.491ms | Execution: 55.842ms | React with ❌ to remove this embed.

ero•2y ago

hm?

Alan72104OP•2y ago

I need the distinct values of them, starting from a1[0]/a2[0] to the last values the 4 is weirdly placed at the last index

rotor_•2y ago

Simplest possible solution would probably be to append the lists and then transform that new list into a set Perhaps chain is a thing in LINQ

Alan72104OP•2y ago

thanks for the idea

rotor_•2y ago

Ok it's called Union it seems Oh actually The Union function actually produces a SET union So it's actually exactly what you need hahah

ero•2y ago

yeah but, why does that matter? you didn't specify that they need to be in order

rotor_•2y ago

Hah reading up it looks like Ero already used that exact function why am I even here lol

Alan72104OP•2y ago

it's updating the top 50 players in the leaderboards of a game and I want to see the top 10 updated results as soon as possible because updating it has a cooldown

ero•2y ago

if speed is a concern, linq is the wrong choice but sure

MODiX•2y ago

Ero#1111

REPL Result: Success

List<int> list1 = new() { 1, 2, 3 };
List<int> list2 = new() { 1, 3, 4 };
List<int> orderedUnion = list1.Union(list2).Order().ToList();

orderedUnion

List<int> list1 = new() { 1, 2, 3 };
List<int> list2 = new() { 1, 3, 4 };
List<int> orderedUnion = list1.Union(list2).Order().ToList();

orderedUnion

Result: List<int>

[
  1,
  2,
  3,
  4
]

[
  1,
  2,
  3,
  4
]

Compile: 543.488ms | Execution: 38.985ms | React with ❌ to remove this embed.

ero•2y ago

should have used your numbers you get the idea

Alan72104OP•2y ago

um not the order of values btw

ero•2y ago

then what are you asking

Alan72104OP•2y ago

in the order of appearance

ero•2y ago

Alan72104OP•2y ago

like in this looping method, starting to add them from index 0 Union() placed the 4 at the last index, which is false obviously bc there are still many different elements after the 4 in a2

ero•2y ago

it's not "false"

Alan72104OP•2y ago

false to my requirements

ero•2y ago

so?

MODiX•2y ago

Ero#1111

REPL Result: Success

int[] a1 = { 1, 2, 3, 5, 6, 7, 8, 9 };
int[] a2 = { 1, 3, 4, 5, 7, 8, 9, 6 };
int[] names2 = a1.Union(a2).Order().ToArray();
names2

int[] a1 = { 1, 2, 3, 5, 6, 7, 8, 9 };
int[] a2 = { 1, 3, 4, 5, 7, 8, 9, 6 };
int[] names2 = a1.Union(a2).Order().ToArray();
names2

Result: int[]

[
  1,
  2,
  3,
  4,
  5,
  6,
  7,
  8,
  9
]

[
  1,
  2,
  3,
  4,
  5,
  6,
  7,
  8,
  9
]

Compile: 498.878ms | Execution: 52.171ms | React with ❌ to remove this embed.

ero•2y ago

what's wrong with this?

Alan72104OP•2y ago

I did some search but still can't find a good way of doing that result should be 1 2 3 4 5 6 7 8 9

ero•2y ago

it is

Alan72104OP•2y ago

well um this method is fine with the example arrays

ero•2y ago

show an example where it isn't fine

MODiX•2y ago

Alan72104#4011

REPL Result: Success

string[] lines1 =
{
"xXDethAngelXx",
"M4LLEY",
"Alan72104",
"varunw14",
"KumoJustBetter",
};
string[] lines2 =
{
"M4LLEY",
"MinionShop",
"xXDethAngelXx",
"Alan72104",
"Calmoniidae",
};

var a = lines1.Union(lines2).ToArray();
a

string[] lines1 =
{
"xXDethAngelXx",
"M4LLEY",
"Alan72104",
"varunw14",
"KumoJustBetter",
};
string[] lines2 =
{
"M4LLEY",
"MinionShop",
"xXDethAngelXx",
"Alan72104",
"Calmoniidae",
};

var a = lines1.Union(lines2).ToArray();
a

Result: string[]

[
  "xXDethAngelXx",
  "M4LLEY",
  "Alan72104",
  "varunw14",
  "KumoJustBetter",
  "MinionShop",
  "Calmoniidae"
]

[
  "xXDethAngelXx",
  "M4LLEY",
  "Alan72104",
  "varunw14",
  "KumoJustBetter",
  "MinionShop",
  "Calmoniidae"
]

Compile: 549.772ms | Execution: 33.969ms | React with ❌ to remove this embed.

MODiX•2y ago

Ero#1111

REPL Result: Success

string[] lines1 =
{
"xXDethAngelXx",
"M4LLEY",
"Alan72104",
"varunw14",
"KumoJustBetter",
};
string[] lines2 =
{
"M4LLEY",
"MinionShop",
"xXDethAngelXx",
"Alan72104",
"Calmoniidae",
};

var a = lines1.Union(lines2).Order().ToArray();
a

string[] lines1 =
{
"xXDethAngelXx",
"M4LLEY",
"Alan72104",
"varunw14",
"KumoJustBetter",
};
string[] lines2 =
{
"M4LLEY",
"MinionShop",
"xXDethAngelXx",
"Alan72104",
"Calmoniidae",
};

var a = lines1.Union(lines2).Order().ToArray();
a

Result: string[]

[
  "Alan72104",
  "Calmoniidae",
  "KumoJustBetter",
  "M4LLEY",
  "MinionShop",
  "varunw14",
  "xXDethAngelXx"
]

[
  "Alan72104",
  "Calmoniidae",
  "KumoJustBetter",
  "M4LLEY",
  "MinionShop",
  "varunw14",
  "xXDethAngelXx"
]

Compile: 524.397ms | Execution: 35.454ms | React with ❌ to remove this embed.

Alan72104OP•2y ago

not ordering that by value but the order of appearance

ero•2y ago

what does that even mean

Alan72104OP•2y ago

first try adding a1[0] then a2[0] then a1[1] then a2[1] I had trouble describing that to google so I came here

ero•2y ago

why does this matter exactly...? i don't understand...

Alan72104OP•2y ago

if the 1st player is being ordered to the last place just because their name starts with "a" and I have 1000 players to update, each taking a 10 sec cooldown I would not be seeing the updated first page of the leaderboard in at least 10 * 1000 secs (the 1st player means the 1st place in the current leaderboard) plus there are 2 leaderboards, that's why I'm doing the distinct and ordering by appearance

Axiss•2y ago

So in your first example, MinionShop would be 3rd?

Alan72104OP•2y ago

yes right

Axiss•2y ago

Gotcha. I don't think LINQ contains a built in method for that

Alan72104OP•2y ago

nope, I googled for a while

MODiX•2y ago

Ero#1111

REPL Result: Success

string[] names1 =
{
"xXDethAngelXx",
"M4LLEY",
"Alan72104",
"varunw14",
"KumoJustBetter"
};

string[] names2 =
{
"M4LLEY",
"MinionShop",
"xXDethAngelXx",
"Alan72104",
"Calmoniidae"
};

string[] zip =
Enumerable.Zip(names1, names2, (n1, n2) => new[] { n1, n2 })
.SelectMany(names => names)
.Distinct()
.ToArray();

zip

string[] names1 =
{
"xXDethAngelXx",
"M4LLEY",
"Alan72104",
"varunw14",
"KumoJustBetter"
};

string[] names2 =
{
"M4LLEY",
"MinionShop",
"xXDethAngelXx",
"Alan72104",
"Calmoniidae"
};

string[] zip =
Enumerable.Zip(names1, names2, (n1, n2) => new[] { n1, n2 })
.SelectMany(names => names)
.Distinct()
.ToArray();

zip

Result: string[]

[
  "xXDethAngelXx",
  "M4LLEY",
  "MinionShop",
  "Alan72104",
  "varunw14",
  "KumoJustBetter",
  "Calmoniidae"
]

[
  "xXDethAngelXx",
  "M4LLEY",
  "MinionShop",
  "Alan72104",
  "varunw14",
  "KumoJustBetter",
  "Calmoniidae"
]

Compile: 635.542ms | Execution: 78.641ms | React with ❌ to remove this embed.

ero•2y ago

does that look right? of course, this is very very bad not performant, unnecessary allocations but it's short and works

Alan72104OP•2y ago

ok ty I will just stay with this yep gotten

ero•2y ago

static class EnumerableExtensions
{
    public static IEnumerable<TSource> ZipManyDistinct<TSource>(
        params IEnumerable<TSource>[] collections)
    {
        return ZipManyDistinct(null, collections);
    }

    public static IEnumerable<TSource> ZipManyDistinct<TSource>(
        IEqualityComparer<TSource>? comparer,
        params IEnumerable<TSource>[] collections)
    {
        comparer ??= EqualityComparer<TSource>.Default;

        IEnumerator<TSource>[] enumerators = new IEnumerator<TSource>[collections.Length];
        HashSet<TSource> set = new(comparer); // set initial capacity?

        try
        {
            for (int i = 0; i < collections.Length; i++)
            {
                enumerators[i] = collections[i].GetEnumerator();
            }

            while (true)
            {
                bool any = false;

                for (int i = 0; i < enumerators.Length; i++)
                {
                    IEnumerator<TSource> enumerator = enumerators[i];

                    if (!enumerator.MoveNext())
                    {
                        continue;
                    }

                    TSource value = enumerator.Current;

                    if (set.Add(value))
                    {
                        yield return value;
                    }

                    any = true;
                }

                if (!any)
                {
                    yield break;
                }
            }
        }
        finally
        {
            for (int i = 0; i < enumerators.Length; i++)
            {
                enumerators[i].Dispose();
            }
        }
    }
}

static class EnumerableExtensions
{
    public static IEnumerable<TSource> ZipManyDistinct<TSource>(
        params IEnumerable<TSource>[] collections)
    {
        return ZipManyDistinct(null, collections);
    }

    public static IEnumerable<TSource> ZipManyDistinct<TSource>(
        IEqualityComparer<TSource>? comparer,
        params IEnumerable<TSource>[] collections)
    {
        comparer ??= EqualityComparer<TSource>.Default;

        IEnumerator<TSource>[] enumerators = new IEnumerator<TSource>[collections.Length];
        HashSet<TSource> set = new(comparer); // set initial capacity?

        try
        {
            for (int i = 0; i < collections.Length; i++)
            {
                enumerators[i] = collections[i].GetEnumerator();
            }

            while (true)
            {
                bool any = false;

                for (int i = 0; i < enumerators.Length; i++)
                {
                    IEnumerator<TSource> enumerator = enumerators[i];

                    if (!enumerator.MoveNext())
                    {
                        continue;
                    }

                    TSource value = enumerator.Current;

                    if (set.Add(value))
                    {
                        yield return value;
                    }

                    any = true;
                }

                if (!any)
                {
                    yield break;
                }
            }
        }
        finally
        {
            for (int i = 0; i < enumerators.Length; i++)
            {
                enumerators[i].Dispose();
            }
        }
    }
}

likely improvable

ero•2y ago

ero•2y ago

Alan72104OP•2y ago

I will probably make it an extension too since I will keep using it for a while ty all

Anton•2y ago

a.Concat(b).Distinct().OrderBy(x => x)

ero•2y ago

not what they want

Accord•2y ago

Was this issue resolved? If so, run /close - otherwise I will mark this as stale and this post will be archived until there is new activity.

Gaming

Programming

❔ LINQ distinct from 2 lists preserving order as soon as they are seen