linq ToArray().Join(...) method is not working?

Question

I have a datatble with one column

I want to concat each filename with wrapper div

something like :

    <div>File Attached : file1 </div>
    <div>File Attached : file2 </div>
    <div>File Attached : file3 </div>
...

I have succedded with :

 string f = String.Join(" ", (from dr in dt.AsEnumerable()
                                                 select "<div>File Attached : " + dr[0].ToString() + "</div>").ToArray<string>());

but didnt success with :

https://i.stack.imgur.com/xCKLD.jpg enter image description here

How can i do it with the .Join method after the ToArray method ?

.Join() method equals to SQL JOIN statement. You need .Aggregate() to accomplish this. — Alex, Jan 09 '12 at 10:58

Lasse Espeholt · Accepted Answer · 2012-01-09T11:09:04.943

2

Join is not the same as String.Join as you have discovered. Enumerable.Join works like joining in databases (but still on local objects, Queryable.Join works with SQL.) An example is given here:

http://msdn.microsoft.com/en-us/library/bb534675.aspx

You could (but I don't recommend it because it will be ambiguous to the user) write an extension method like this:

public static class StringExtensions
{
    public string Join(this IEnumerable<string> source, string sep)
    {
        return string.Join(sep, source.ToArray()); // You can erase `.ToArray()` if you're using .Net 4
    }
}

and then it would work with (...).Join(" ").

My solution: (4.0)

var query = from dr in dt.AsEnumerable() // You may be able to erase `AsEnumerable` depending on your source
            select "<div>File Attached : " + dr[0] + "</div>";
var f = string.Join(" ", query);

My solution: (3.5)

var arr = dt.AsEnumerable()
            .Select(dr => "<div>File Attached : " + dr[0] + "</div>")
            .ToArray();
var f = string.Join(" ", arr);

edited Jan 09 '12 at 11:09

answered Jan 09 '12 at 10:54

Lasse Espeholt

17,622
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oh sh*t , is it the sql join for linq? – Royi Namir Jan 09 '12 at 10:56
@RoyiNamir: Yes, to get the same result using LINQ you should use `.Aggregate(...)`, but it's more difficult and less clear than `string.Join` – digEmAll Jan 09 '12 at 10:57
Yes, and `Aggregate` is inefficient with the naive `+` solution as given in another answer. **Always use `string.Join`.** – Lasse Espeholt Jan 09 '12 at 11:00
@lasseespeholt , OK but doesnt Array type has his own Join method ? – Royi Namir Jan 09 '12 at 11:01
@RoyiNamir No, see http://stackoverflow.com/questions/484464/array-join-in-net . `Join` is only an extension method. – Lasse Espeholt Jan 09 '12 at 11:02

score 1 · Answer 2 · answered Jan 09 '12 at 10:57

1

Are you sure that that the Join function is the correct one? It sounds like you could be using the Aggregate function to end up with the same result, like this:

dt.AsEnumerable().Aggregate(string.Empty, (x,y) => x + string.Format("<div>File Attached : {0} </div>", y));

answered Jan 09 '12 at 10:57

A. Tapper

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OK but doesnt Array type has his own Join method ? – Royi Namir Jan 09 '12 at 11:01

linq ToArray().Join(...) method is not working?

2 Answers2