LINQ to Populate a range

问题

I can't figure out how to do the second part of this (the for/foreach) with a LINQ expressions and haven't found any similar examples with LINQ. rangeDays will be between about 5 and 200, and q1 is a list of MyClasses where RowID is about from 10000 to 25000, without gaps.

public class MyClass { public int RowID; public object otherData; }

PopulateRange(int rangeDays, List<MyClass> q1){
var q2 = (from a in q1 
        let Rows = new int[rangeDays]
        select new {a.RowID, Rows }).ToList();
foreach(var a in q2)
{
    for(int i = 0; i < rangeDays; i++)
    {
        a.Rows[i] = a.RowID + i;
    }
}

Thanks in advance.

Update: I got this running with 2 linq statements as shown below (hopefully this is all runnable this time).

public List<MyClass> PopulateRange(int rangeDays, IQueryable<TheirClass> q1)
{
    var q2 = (from a in q1 
                select new MyClass()
                { RowID = a.RowID, Rows = new int[rangeDays] }).ToList();
    q2.ForEach(a => a.Rows = Enumerable.Range(0, rangeDays).
                Select(i => i + a.RowID).ToArray());
    return q2;
}
public class MyClass
{
    public int RowID;
    public int[] Rows;
}
public class TheirClass
{
    public int RowID;
    public int ID;
    public string Symb;
    public DateTime? EventTime;
    public decimal? Value;
}

This is acceptable, but does anyone know why the following single statement throws a NotSupportedException "Local sequence cannot be used in LINQ to SQL implementations of query operators except the Contains operator." when I try to compile & run:

public List<MyClass> PopulateRange(int rangeDays, IQueryable<TheirClass> q1)
{
    var q2 = (from a in q1 
                select new MyClass() 
        { RowID = a.RowID, Rows = Enumerable.Range(0, rangeDays).
        Select(i => i + a.RowID).ToArray() }).ToList();
    return q2;
}

回答1:

A slight variation on Ani's answer:

var q2 = q1.Select(a => new { Rows = Enumerable.Range(a.RowID, rangeDays)
                                               .ToArray(),
                              RowID = a.RowID });

Differences:

When there's just a single select, I don't bother with query expression syntax
Rather than using Range from 0 and then Select, I figured it would be easier to just start off at a.RowID :)

回答2:

I think q1's type should actually be List<MyRowClass> or similar (it certainly can't be a List<int>). You probably want:

var q2 = (from a in q1
          select new
          {
              a.RowID,
              Rows = Enumerable.Range(0, rangeDays)
                               .Select(i => i + a.RowID)
                               .ToArray()

          }).ToList();

来源：https://stackoverflow.com/questions/4914638/linq-to-populate-a-range

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linq

foreach

range

let