Join collection of objects into comma-separated string

Question

In many places in our code we have collections of objects, from which we need to create a comma-separated list. The type of collection varies: it may be a DataTable from whi

Answer 1

static string ToCsv<T>(IEnumerable<T> things, Func<T, string> toStringMethod)
{
    StringBuilder sb = new StringBuilder();

    foreach (T thing in things)
        sb.Append(toStringMethod(thing)).Append(',');

    return sb.ToString(0, sb.Length - 1); //remove trailing ,
}

Use like this:

DataTable dt = ...; //datatable with some data
Console.WriteLine(ToCsv(dt.Rows, row => row["ColName"]));

or:

List<Customer> customers = ...; //assume Customer has a Name property
Console.WriteLine(ToCsv(customers, c => c.Name));

I don't have a compiler to hand but in theory it should work. And as everyone knows, in theory, practice and theory are the same. In practice, they're not.

Answer 2

As an aside: The first modification I would make is to use the StringBuilder Class instead of just a String - it'll save resources for you.

Answer 3

string.Join(", ", Array.ConvertAll(somelist.ToArray(), i => i.ToString()))

Answer 4

// using System.Collections;
// using System.Collections.Generic;
// using System.Linq

public delegate string Indexer<T>(T obj);

public static string concatenate<T>(IEnumerable<T> collection, Indexer<T> indexer, char separator)
{
    StringBuilder sb = new StringBuilder();
    foreach (T t in collection) sb.Append(indexer(t)).Append(separator);
    return sb.Remove(sb.Length - 1, 1).ToString();
}

// version for non-generic collections
public static string concatenate<T>(IEnumerable collection, Indexer<T> indexer, char separator)
{
    StringBuilder sb = new StringBuilder();
    foreach (object t in collection) sb.Append(indexer((T)t)).Append(separator);
    return sb.Remove(sb.Length - 1, 1).ToString();
}

// example 1: simple int list
string getAllInts(IEnumerable<int> listOfInts)
{
    return concatenate<int>(listOfInts, Convert.ToString, ',');
}

// example 2: DataTable.Rows
string getTitle(DataRow row) { return row["title"].ToString(); }
string getAllTitles(DataTable table)
{
    return concatenate<DataRow>(table.Rows, getTitle, '\n');
}

// example 3: DataTable.Rows without Indexer function
string getAllTitles(DataTable table)
{
    return concatenate<DataRow>(table.Rows, r => r["title"].ToString(), '\n');
}

Answer 5

Here's my favorite answer adapted to the question, and corrected Convert to ConvertAll:

string text = string.Join(", ", Array.ConvertAll(table.Rows.ToArray(), i => i["title"]));

Answer 6

You could write a function that transforms a IEnumerable into a comma separated string

public string Concat(IEnumerable<string> stringList)
{
    StringBuilder textBuilder = new StringBuilder();
    string separator = String.Empty;
    foreach(string item in stringList)
    {
        textBuilder.Append(separator);
        textBuilder.Append(item);
        separator = ", ";
    }
    return textBuilder.ToString();
}

You can then use Linq to query your collection/dataset/etc to provide the stringList.