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

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

public delegate string Indexer(T obj);

public static string concatenate(IEnumerable collection, Indexer 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(IEnumerable collection, Indexer 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 listOfInts)
{
    return concatenate(listOfInts, Convert.ToString, ',');
}

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

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