如何使用C＃的LINQ功能执行以下操作？

Question

I need help with the following statement to be converted to lambda statement how do i do it?

for (int row = 0; row < rows; row++)
{
    for (int column = 0; column < columns; column++)
    {
        gList.Add(new G(this, new L(row, column), 0, 20, 30));
    }
}

thanks for all the help!!!

Answer 1

var gList = Enumerable.Range(0, rows)
    .SelectMany(row =>
        Enumerable.Range(0, columns)
            .Select(column => new G(this, new L(row, column), 0, 20, 30)
        )
    ).ToList() or .ToArray();

SelectMany will flatten the Enumerable returned from the Select into an IEnumerable.

Answer 2

var gList = from row in Enumerable.Range(0, rows)
            from col in Enumerable.Range(0, columns)
            select new G(this, new L(row, col), 0, 20, 30)

My favourite for inline cartesians like this

Answer 3

List<G> gList = Enumerable.Range(0, rows)
    .SelectMany(row => Enumerable.Range(0, columns)
        .Select(col => new G(this, new L(row, col), 0, 20, 30)))
    .ToList();

Answer 4

Give me the indexes, project each index to a new L , project each L to a new G and assign the resulting sequence of objects to a list named gList .

var indexes = from row in Enumerable.Range(0, rows)
              from column in Enumerable.Range(0, columns)
              select new { Row = row, Column = column };
var ls = indexes.Select(index => new L(index.Row, index.Column));
var gs = ls.Select(l => new G(this, l, 0, 20, 30)).ToList();
var gList = gs.ToList();

Note that if gList is an existing list that you want to add to you can replace the last line by

gList.AddRange(gs);

It reads exactly like what it is doing.

Answer 5

As you can see from the other answers, using lambdas don't always result in cleaner code. Unless you have a specific reason for using lambdas in this case, I would leave the for loops as is.

Readability should be your primary concern, but I imagine using a normal for loop might be slightly faster because you don't have the overhead of function calls, but the difference in most cases won't matter.

Answer 6

Putting everything into one single expression would lead to terrible code. Why would you do that? Does the following help: (untested, out of my head)

public IEnumerable<L> GenerateLs(int rows, int columns)
{
    for (int row = 0; row < rows; row++)
    {
        for (int column = 0; column < columns; column++)
        {
            yield return new L(row, column);
        }
    }
}

gList.Add(l => GenerateLs(rows,columns).Select(new G(this,l,0,20,30)));