动态更改月份列表

Question

我遇到了一个需求。 我从database 得到两个标志，即lastMonthNumber 和lastMonthName，它们的范围可以是1 to 12 和January to December。 现在我有一个要求，如果lastMonthName="March"和lastMonthNumner=12，那么父list应该如下：

1, April
2, May
3, June
4, July
5, August
6, September
7, October
8, November
9, December
10, January
11, February
12, March

如果lastMonthName="April" 和lastMonthNumber=6，那么列表应该是：

7, November
8, December
9, January
10, February
11, March
12, April

这个lastMonthNumber 的范围可以是1 to 12 和lastMonthName 也可以是Jan to Dec。父 list 需要是动态的。

如果lastMonthNumber=6 和lastMonthName="April"，则list 需要有 6 个元素，其中 April 为 12，并且回溯总共有 6 个元素。

父list可以是dictionary，如：

var monthsDictionary=new Dictionary<int, string>();

我正在尝试以下操作，但无法进一步可视化：

var monthsDictionary = new Dictionary<int, string>();
var numbers = new List<int> { 1,2,3,4,5,6,7,8,9,10,11,12};
var months = new List<string> {"January","February","March","April","May","June","July","August","September","October","November","December" };
 foreach (var month in months.Select())
     {
         if (month == lastMonthName)
            {

            }
      }

请帮忙。指针会很有帮助。

Answer 1

有一个带有月份名称的常量

private readonly string[] monthNames = { "Januar" ..., "December" };

以及能够循环索引的访问器方法：

private string GetMonthName(int index)
{
  if (index < 0) return monthNames[monthNames.Length - 1 - (index % monthNames.Length)];
  return monthNames[index % monthNames.Length];
}

然后创建列表：

int indexOfLastMonthName = Array.IndexOf(monthNames, lastMonthName);

var parentData = Enumerable
  // Create as many items as last month number
  .Range(0, lastMonthNumber)

  // Create the list in reverse order, start on LastMonthName and 12,
  // then go back with every item
  .Select(x => new 
  { 
    Number = 12 - x, 
    Name = GetMonthName(indexOfLastMonthName - x)
  }

  // Turn it back
  .Reverse();

然后将其填充到适当的数据结构中。例如像这样：

List<Tuple<int, string>> parentList = parentData
  .Select(x => Tuple.Create(x.Number, x.Name)))
  .ToList();

---

如果您更喜欢经典解决方案（使用上面的 GetMonthName 方法）：

int indexOfLastMonthName = Array.IndexOf(monthNames, lastMonthName);
List<Tuple<int, string>> parentList = new List<Tuple<int, string>>();

for(int i = 0; i < lastMonthNumber; i++)
{
  parentList.Add(
    Tuple.Create(
      12 - i, 
      GetMonthName(indexOfLastMonthName - i));
}

parentList.Reverse();

Answer 2

试试这个 linq 查询

var months = new List<string> {"January","February","March","April","May","June","July","August","September","October","November","December" };

var lastMonthNumber = ...;
var lastMonthName = ....;

var rows = months.Concat(months)
    .Reverse()
    .SkipWhile(m => m != lastMonthName)
    .Take(lastMonthNumber)
    .Reverse()
    .Select((m, i) => new { id = i + 12 - lastMonthNumber + 1, m})
    .ToArray();

它复制了一个月份列表，反转它并跳过项目，直到找到lastMonthName。之后，此代码限制结果项计数为 lastMonthNumber 并反向列出

Answer 3

试试下面的小提琴。 https://dotnetfiddle.net/GYP2Go

private static Dictionary<int, string> GetRequiredResult(int lastMonthNumber, string lastMonthName)
{
    var indx =  months.IndexOf(lastMonthName);

    // here this list will have months in required order that ends with lastMonthName
    var revisedMonthList = new List<string>();
    revisedMonthList.AddRange(months.Skip(indx + 1).Take(12));
    revisedMonthList.AddRange(months.Take(indx + 1));

    // get count = lastMonthNumber element from last using index, and then convert them to dictionary.
    return revisedMonthList
        .Select((mn, index) => new {index, mn})
        .Where(c => c.index >= months.Count - lastMonthNumber)
        .ToDictionary(c=>c.index + 1, c=>c.mn); 
}

Answer 4

    var monthsDictionary = new Dictionary<int, string>();
    var numbers = new List<int> { 1,2,3,4,5,6,7,8,9,10,11,12};
    var months = new List<string> {"January","February","March","April","May","June","July","August","September","October","November","December" };
int flag=0;
int items=12;
var numbersList = new List<int>();
var monthsList = new List<string>(); 
     foreach (var month in months)
         {
            if(flag==0){
             monthsList.Insert(items--,month);
             if (month == lastMonthName)
                {
                    flag=1;
                }
}
         else if(flag==1)
         {
           monthsList.add(month);
          }
          }
flag=0;

Answer 5

尝试以下：

        var months = Enumerable.Range(1, 12).Select(i => new
        {
            I = i,
            M = System.Globalization.DateTimeFormatInfo.CurrentInfo.GetMonthName(i)
        });

        //string lastMonthName = "March"; int lastMonthNumber = 12;
        //string lastMonthName = "April"; int lastMonthNumber = 6;
        var selMonthInt = months.Where(x => x.M == lastMonthName).Select(y => y.I).FirstOrDefault();
        int endCount = lastMonthNumber + selMonthInt;
        if (endCount >= 12) { endCount = selMonthInt; }

        var lst1 = months.Where(x => x.I > endCount).Select(z => z.M);
        var lst2 = months.Where(x => x.I <= selMonthInt).Select(z => z.M);
        var lst = lst1.Union(lst2).ToArray();

        var selMonths = Enumerable.Range(0, lastMonthNumber).Select(i => new { I = (13 - lastMonthNumber + i), M = lst[i] });