Using LINQ to select a byte array

Question

I'm having some trouble selecting a byte[] from inside of a list of objects model is setup as:

public class container{
    public byte[] image{ get;set; }
    //some other irrelevant properties    
}

in my controller I have:

public List<List<container>> containers; //gets filled out in the code

i'm trying to pull image down one level so I am left with a List<List<byte[]>> using LINQ so far I have:

var imageList = containers.Select(x => x.SelectMany(y => y.image));

but it is throwing:

cannot convert from 
'System.Collections.Generic.IEnumerable<System.Collections.Generic.IEnumerable<byte>>' to 
'System.Collections.Generic.List<System.Collections.Generic.List<byte[]>>'

Apparently it is selecting the byte array as a byte?

Some guidance would be appreciated!

Firstly, it would be a really good idea to follow .NET naming conventions, e.g. Container and Image. — Jon Skeet
– Jon Skeet, Commented Nov 24, 2014 at 20:09
@Jon- sorry these are dummy names not copy/pasted from my code — nealruggles1
– nealruggles1, Commented Nov 24, 2014 at 20:33
If you're using better names in your code, then please use better names in your examples, too. Anything unconventional detracts from the readability of the code - and even though this code isn't going into production, you're still asking people to read it. — Jon Skeet
– Jon Skeet, Commented Nov 24, 2014 at 21:03
Ah yes I completely didn't consider that. I'll keep that in mind in the future! Thanks for your help — nealruggles1
– nealruggles1, Commented Nov 24, 2014 at 21:24

Jon Skeet · Accepted Answer · 2014-11-24 20:10:42Z

13

You don't want SelectMany for the image property - that's going to give a sequence of bytes. For each list of containers, you want to transform that to a list of byte arrays, i.e.

innerList => innerList.Select(c => c.image).ToList()

... and then you want to apply that projection to your outer list:

var imageList = containers.Select(innerList => innerList.Select(c => c.image)
                                                        .ToList())
                          .ToList();

Note the calls to ToList in each case to convert an IEnumerable<T> to a List<T>.

answered Nov 24, 2014 at 20:10

Jon Skeet

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