CODEWITHSUNDEEP
c#linq
Maro
Maro

Reputation: 2629

Linq Select specific properties from list to 2d array

I have list of objects that i want to export to excel:

//My export to excel function:
public static void ExportToExcel(string[,] data, string excelFilePath = null)
{
  // .....
}

My list contains many columns so i would like to select specific columns and add them into 2d array, also add the header on the top

public class Student

{
    public int Id { get; set; }
    public string Name { get; set; }
    public int Age { get; set; }
    public Address Adress { get; set; }
    public Evaluation Evaluation { get; set; }
    // ... many more
}

List:

>   IEnumerable<Student> students

Fields to be selected:

  1. Id
  2. Name
  3. Address.Zipcode

I can perform this with for loop however i'm interested in linq, also i would like to hear your advice about performance since the list has + 200k records

Edit Sample

Columns => ID Name Zipcode

Rows => values

ID Name Zip
1  Mike 1101 
2  Jan  2250
3  Peter 4456

Upvotes: 0

Views: 2668

Answers (4)

user5539403
user5539403

Reputation:

You can create another class with just the columns you want, say LiteStudent

Then use something like this.

students.select(x => new LiteStudent{
 Id = x.Id,
 Name = x.Name,
 ZipCode = x.Address.ZipCode
}).ToArray();

Or creating no new class at all

students.select(x => new {
 Id = x.Id,
 Name = x.Name,
 ZipCode = x.Address.ZipCode
}).ToArray();

Edit: If you want to convert to a 2D string array, follow the answer by Hari Prasad.

As for performance, you may want to take a look at this answer, it might be possible to use multi-threading to speed up processing of large data somehow.

If not limited to Linq, we can divide the list into smaller lists and create multiple threads to assign data in parallel, each thread process a part of the list.

Upvotes: 0

Jens Hunt
Jens Hunt

Reputation: 36

You can do something like this

class YourNewStuff
{
    public int Id { get; set; }
    public string Name { get; set; }
    public string Zip { get; set; }
}

var newstuff2 = new List<YourNewStuff>();

students.Select(x => newstuff2.Add(new YourNewStuff()
{
    Id = x.Id,
    Name = x.Name,
    Zip = x.Adress.Zip
});

Upvotes: 0

Keyur PATEL
Keyur PATEL

Reputation: 2329

I think I understand why you need the 2d array. I ran into the same issue when exporting hundreds of records using linq and interop.Excel

Here is a brief overview of what I did:

var list = students.Select(i => new { i.Id, i.Name, i.Address.Zipcode }).ToList();
int i=0;
foreach (var stud in list)
{
    data[i, 0] = stud.Id;
    data[i, 1] = stud.Name;
    data[i, 2] = stud.Address.Zipcode;
    i++;
}

Then use the data array to convert into excel range by using Excel.Range.set_Value. In my code, I used a 2d array of objects instead of strings since set_Value only accepts array of objects.

testRng.set_Value(Excel.XlRangeValueDataType.xlRangeValueDefault, data);

where testRng is an Excel.Range

Upvotes: 3

Hari Prasad
Hari Prasad

Reputation: 16956

You could deal with Jagged Arrays and do something like this, there is no direct way of creating multi dimensional array with in Linq (At least that I'm aware), so try using Array of Arrays. 

var result = students.Select(x=> new string[] 
                                 {
                                      x.Id.ToString(), 
                                      x.Name, 
                                      x.Address.ZipCode
                                 })
                     .ToArray();

Still keen and not interested in changing function definition? Well, you could use this logic to convert result to Multi dimensional array.

Upvotes: 2

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