Question

I have a query in linq but i am unable to understand it, because i didn’t write this query. The query is below

string[] arr1 = new string[]
                        {
                            "Pakistan:4,India:3,USA:2,Iran:1,UK:0",
                            "Pakistan:4,India:3,USA:2,Iran:1,UK:0",
                            "India:4,USA:3,Iran:2,UK:1,Pakistan:0"
                        };

        var count = arr1
            .SelectMany(s => s.Split(new[] { ',' }, StringSplitOptions.RemoveEmptyEntries))
            .GroupBy(s => s.Split(':')[0], s => s.Split(':')[1])
            .ToDictionary(g => g.Key,
                 g =>
                 {
                     var items = g.Distinct();
                     var result = new Dictionary<String, int>();
                     foreach (var item in items)
                         result[item] = g.Count(gitem => gitem == item);
                     return result;
                 });


        // print the result
        foreach (var country in count.Keys)
        {
            foreach (var ocurrence in count[country].Keys)
            {
                Console.WriteLine("{0} : {1} = {2}", country, ocurrence, count[country][ocurrence]);
            }
        }

Purpose of this query

this query is performed to achieve this: We want to know that how many times Pakistan comes with ‘0’ , how many times with ‘1’ ,2 ,3 , 4 , and we want to get this information for all countries . Please can anyone define it step by step .Thanks

Note : this query is compiled , has no errors and is working properly

Answer 1

Let’s look at the query, step by step

SelectMany takes the result of splitting on ‘,’ and combines the various splits back into a single IEnumerable

Projects each element of a sequence to an IEnumerable and flattens the resulting sequences into one sequence.

So at that stage, you have converted the array arr1 into a single IEnumerable<string> with values like like USA:2

GroupBy then groups that IEnumberable<string>. It splits each entry like USA:2 using the ‘:’ character. The left-hand side is the grouping key and the right-hand side is the value.

Groups the elements of a sequence according to a specified key selector function.

ToDictionary transforms that grouping into a Dictionary. The key of the Dictionary entry is the grouping key (e.g. USA). The value of the Dictionary entry is a new (anonymous) object:

g =>
             {
                 var items = g.Distinct();
                 var result = new Dictionary<String, int>();
                 foreach (var item in items)
                     result[item] = g.Count(gitem => gitem == item);
                 return result;
             }

The anonymous object is constructed by going through and counting the unique occurrences of a given count (e.g. if the key is USA, how many times is the value 1) and returns that count.