将对象集合加入逗号分隔的字符串中

Question

在我们的代码中的许多地方,我们都有对象集合,我们需要从中创建以逗号分隔的列表.集合的类型各不相同:它可能是我们需要某个列的DataTable,或者是List <Customer>等.

现在我们遍历集合并使用字符串连接,例如:

string text = "";
string separator = "";
foreach (DataRow row in table.Rows)
{
    text += separator + row["title"];
    separator = ", ";
}

这有更好的模式吗？理想情况下,我希望通过发送函数来从每个对象获取正确的字段/属性/列,我们可以重用一种方法.

Answer 1

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

Answer 2

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 ,
}

使用这样:

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

要么:

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

我没有编译器,但理论上它应该工作.众所周知,理论上,实践和理论都是一样的.在实践中,他们不是.

Answer 3

// 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 4

我发现string.Join和Lambda Select>有助于编写最小代码.

        List<string> fruits = new List<string>();
        fruits.Add("Mango");
        fruits.Add("Banana");
        fruits.Add("Papaya");

        string commaSepFruits = string.Join(",", fruits.Select(f => "'" + f + "'"));
        Console.WriteLine(commaSepFruits);

        List<int> ids = new List<int>();
        ids.Add(1001);
        ids.Add(1002);
        ids.Add(1003);

        string commaSepIds = string.Join(",", ids);
        Console.WriteLine(commaSepIds);

        List<Customer> customers = new List<Customer>();
        customers.Add(new Customer { Id = 10001, Name = "John" });
        customers.Add(new Customer { Id = 10002, Name = "Robert" });
        customers.Add(new Customer { Id = 10002, Name = "Ryan" });

        string commaSepCustIds = string.Join(", ", customers.Select(cust => cust.Id));
        string commaSepCustNames = string.Join(", ", customers.Select(cust => "'" + cust.Name + "'"));

        Console.WriteLine(commaSepCustIds);
        Console.WriteLine(commaSepCustNames);

        Console.ReadLine();

Answer 5

您可以编写一个将IEnumerable转换为逗号分隔字符串的函数

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();
}

然后,您可以使用Linq查询集合/数据集/ etc以提供stringList.

Answer 6

在.NET 4中,您可以这样做 string.Join(", ", table.Rows.Select(r => r["title"]))