Question

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Compare two Lists for differences

I have following set of arrays

string[] arr1 = { 1155717, 5184305, 2531291, 1676341, 1916805 ... } 
string[] arr2 = { 1155717, 1440230, 2531291, 8178626, 1916805 ... }
string[] arr3 = { 1155717, 5184305, 4025514, 1676341, ... }

Arrays count is in millions & can contains characters as well.
I want to create a report like this in csv

diff.csv

arr1,arr2,arr3
1155717,1155717,1155717
5184305,--N/A--,5184305
--N/A--,1440230,--N/A--
--N/A--,--N/A--,4025514
1676341,--N/A--,1676341
--N/A--,8178626,--N/A--
1916805,1916805,--N/A--

I guess applying for loops in each & comparing wouldn’t be that good approach.Any Ideas?

Few Things i missed :
1. Order doesnt matter.
2. Elements in a single list will be unique.
3. I plan to skip loops as far as possible & look for .NET 3.5 / 4.0 ‘s new features in LINQ / Generics which I can apply here!

For those voting negatively or closing this question please explain so?

Answer 1

You can use linq to GroupJoin:

string[] arr1 = { "1155717", "5184305", "2531291", "1676341", "1916805" };
string[] arr2 = { "1155717", "1440230", "2531291", "8178626", "1916805" };
string[] arr3 = { "1155717", "5184305", "4025514", "1676341" };

var allPossibleTerms = arr1.Union(arr2).Union(arr3);

allPossibleTerms
    .GroupJoin(arr1, all => all, a1 => a1, (all, a1) => new { Number = all, A1 = a1 })
    .SelectMany(joined => joined.A1.DefaultIfEmpty(), (collection, result) => new { collection.Number, A1 = result})
    .GroupJoin(arr2, joined => joined.Number, a2 => a2, (collection, a2) => new { Number = collection.Number, A1 = collection.A1, A2 = a2 })
    .SelectMany(joined => joined.A2.DefaultIfEmpty(), (collection, result) => new { collection.Number, A1 = collection.A1, A2 = result})
    .GroupJoin(arr3, joined => joined.Number, a3 => a3, (collection, a3) => new { Number = collection.Number, A1 = collection.A1, A2 = collection.A2, A3 = a3 })
    .SelectMany(joined => joined.A3.DefaultIfEmpty(), (collection, result) => new { collection.Number, A1 = collection.A1, A2 = collection.A2, A3 = result});;

Basically, this creates a master-list of all terms, and joins each array as it goes.

╔══════════════════════════════════════╗
║ Number   A1       A2       A3        ║
╠══════════════════════════════════════╣
║ 1155717  1155717  1155717  1155717   ║
║ 5184305  5184305  -------  5184305   ║
║ 2531291  2531291  2531291  -------   ║
║ 1676341  1676341  -------  1676341   ║
║ 1916805  1916805  1916805  -------   ║
║ 1440230  -------  1440230  -------   ║
║ 8178626  -------  8178626  -------   ║
║ 4025514  -------  -------  4025514   ║
╚══════════════════════════════════════╝