How to select multiple elements into array in Linq query?

Question

Net core application. I have below query in my application

 var result  = sourceProposal.Quotes
      .Where(x=>x.QuotationId == sourceQuoteId)
      .FirstOrDefault()
      .QuoteLines.Select(x=>(x.Quantity,x.WtgType)).ToArray();

This yields in two array elements such as

0 element   1, "string1"
1 element   2, "string2"

What I am expecting is

(int[] sourceQuantity, string[] destinationTurbineType) = sourceProposal.Quotes
           .Where(x=>x.QuotationId == sourceQuoteId)
           .FirstOrDefault()
           .QuoteLines.Select(x=>(x.Quantity,x.WtgType)).ToArray();

I want to copy to tuple which has int[] sourceQuantity, string[] destinationTurbineType this piece of code is not working and throwing error does not contain definition for destructor and no accessible extension method Descontruct accepting first argument of type int(sourceQuantity, string destinationTurbineType)[].

Can someone help me to copy values to sourceQuantity and destinationTurbineType. Any help would be appreciated. Thanks

"What I am expecting is" - why are you expecting this?

Guru Stron
– Guru Stron

2022-05-06 11:27:39 +00:00
Commented May 6, 2022 at 11:27 — Guru Stron
– Guru Stron, Commented May 6, 2022 at 11:27

Guru Stron · Accepted Answer · 2022-05-06 12:07:50Z

3

Select<TSource,TResult> returns enumerable/queryable of the type returned by selector (IEnumerabe<TResult>/IQueryable <TResult>).

If you want to achieve this with LINQ you can use Aggregate:

// note that sourceQuantity and destinationTurbineType would be lists, not arrays
var (sourceQuantity, destinationTurbineType) = sourceProposal.Quotes
    .Where(x=>x.QuotationId == sourceQuoteId)
    .FirstOrDefault()
    .QuoteLines
    .Aggregate((ints: new List<int>(), strs: new List<string>()), (aggr, curr) =>
    {
        aggr.ints.Add(curr.Quantity);
        aggr.strs.Add(curr.WtgType);
        return aggr;
    });

Or just use simple for loop and copy data to destination arrays (possibly move to some extension method). Something along this lines:

var quoteLines = sourceProposal.Quotes
    .Where(x=>x.QuotationId == sourceQuoteId)
    .FirstOrDefault()
    .QuoteLines; // assuming it is materialized collection with indexer like an array or list
int[] sourceQuantity = new int[quoteLines.Length]; // or Count
string[] destinationTurbineType = new string[quoteLines.Count()];
for(int i = 0; i < quoteLines.Length; i++)
{
   var curr = quoteLines[i];
   sourceQuantity[i] = curr.Quantity;
   destinationTurbineType[i] = curr.WtgType;
}

edited May 6, 2022 at 12:07

answered May 6, 2022 at 11:36

Guru Stron

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7 Comments

sr28 Over a year ago

Could you shorten this by removing the Where and doing the match on QuotationId in the FirstOrDefault?

Guru Stron Over a year ago

@sr28 yes. The original code has also a problem with Default part.

Mr Perfect Over a year ago

Hi Thanks for your answer, It is working, May I know if there is any issue with original code

Guru Stron Over a year ago

@MrPerfect was glad to help! FirstOrDefault will return null if the type is reference type and nothing was matched, so .FirstOrDefault().QuoteLines will throw NRE.

Peter Csala Over a year ago

resultSelector: acc => (acc.ints.ToArray(), acc.strs.ToArray() will convert the lists to arrays

|

Clinton · Accepted Answer · 2022-05-06 11:48:22Z

Currently there is no built-in LINQ method to do this. But you could write your own extension method. Something like the following:

public static class EnumerableExtensions
{
    public static (TFirst[] xs, TSecond[] ys) Unzip<TFirst, TSecond>(this IEnumerable<(TFirst, TSecond)> zipped)
    {
        var xs = new List<TFirst>();
        var ys = new List<TSecond>();
        foreach (var (x, y) in zipped)
        {
            xs.Add(x);
            ys.Add(y);
        }
        return (xs.ToArray(), ys.ToArray());
    }
}

var (xs, ys) =
    new[] { 1, 2, 3 }
    .Zip(new[] { "a", "b", "c" })
    .Unzip();

Console.WriteLine(string.Join(", ", xs)); // 1, 2, 3
Console.WriteLine(string.Join(", ", ys)); // a, b, c

Or in the case of your example, you could then use:

(int[] sourceQuantity, string[] destinationTurbineType) = sourceProposal.Quotes
           .Where(x=>x.QuotationId == sourceQuoteId)
           .FirstOrDefault()
           .QuoteLines.Select(x=>(x.Quantity,x.WtgType)).Unzip();

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