C#: Cleanest way to divide a string array into N instances N items long

Question

I know how to do this in an ugly way, but am wondering if there is a more elegant and succinct method.

I have a string array of e-mail addresses. Assume the string

Answer 1

I would just loop through the array and using StringBuilder to create the list (I'm assuming it's separated by ; like you would for email). Just send when you hit mod 50 or the end.

void Foo(string[] addresses)
{
    StringBuilder sb = new StringBuilder();

    for (int i = 0; i < addresses.Length; i++)
    {
        sb.Append(addresses[i]);
        if ((i + 1) % 50 == 0 || i == addresses.Length - 1)
        {
            Send(sb.ToString());
            sb = new StringBuilder();
        }
        else
        {
            sb.Append("; ");
        }
    }
}

void Send(string addresses)
{
}

Answer 2

I think we need to have a little bit more context on what exactly this list looks like to give a definitive answer. For now I'm assuming that it's a semicolon delimeted list of email addresses. If so you can do the following to get a chunked up list.

public IEnumerable<string> DivideEmailList(string list) {
  var last = 0;
  var cur = list.IndexOf(';');
  while ( cur >= 0 ) {
    yield return list.SubString(last, cur-last);
    last = cur + 1;
    cur = list.IndexOf(';', last);
  }
}

public IEnumerable<List<string>> ChunkEmails(string list) {
  using ( var e = DivideEmailList(list).GetEnumerator() ) {
     var list = new List<string>();
     while ( e.MoveNext() ) {
       list.Add(e.Current);
       if ( list.Count == 50 ) {
         yield return list;
         list = new List<string>();
       }
     }
     if ( list.Count != 0 ) {
       yield return list;
     }
  }
}

Answer 3

I think this is simple and fast enough.The example below divides the long sentence into 15 parts,but you can pass batch size as parameter to make it dynamic.Here I simply divide using "/n".

 private static string Concatenated(string longsentence)
 {
     const int batchSize = 15;
     string concatanated = "";
     int chanks = longsentence.Length / batchSize;
     int currentIndex = 0;
     while (chanks > 0)
     {
         var sub = longsentence.Substring(currentIndex, batchSize);
         concatanated += sub + "/n";
         chanks -= 1;
         currentIndex += batchSize;
     }
     if (currentIndex < longsentence.Length)
     {
         int start = currentIndex;
         var finalsub = longsentence.Substring(start);
         concatanated += finalsub;
     }
     return concatanated;
 }

This show result of split operation.

 var parts = Concatenated(longsentence).Split(new string[] { "/n" }, StringSplitOptions.None);

Answer 4

It sounds like the input consists of separate email address strings in a large array, not several email address in one string, right? And in the output, each batch is a single combined string.

string[] allAddresses = GetLongArrayOfAddresses();

const int batchSize = 50;

for (int n = 0; n < allAddresses.Length; n += batchSize)
{
    string batch = string.Join(";", allAddresses, n, 
                      Math.Min(batchSize, allAddresses.Length - n));

    // use batch somehow
}

Answer 5

Extensions methods based on Eric's answer:

public static IEnumerable<IEnumerable<T>> SplitIntoChunks<T>(this T[] source, int chunkSize)
{
    var chunks = from index in Enumerable.Range(0, source.Length)
                 group source[index] by index / chunkSize;

    return chunks;
}

public static T[][] SplitIntoArrayChunks<T>(this T[] source, int chunkSize)
{
    var chunks = from index in Enumerable.Range(0, source.Length)
                 group source[index] by index / chunkSize;

    return chunks.Select(e => e.ToArray()).ToArray();
}

Answer 6

Seems similar to this question: Split a collection into n parts with LINQ?

A modified version of Hasan Khan's answer there should do the trick:

public static IEnumerable<IEnumerable<T>> Chunk<T>(
    this IEnumerable<T> list, int chunkSize)
{
    int i = 0;
    var chunks = from name in list
                 group name by i++ / chunkSize into part
                 select part.AsEnumerable();
    return chunks;
}

Usage example:

var addresses = new[] { "a@example.com", "b@example.org", ...... };

foreach (var chunk in Chunk(addresses, 50))
{
    SendEmail(chunk.ToArray(), "Buy V14gr4");
}