在linq中生成步长的数字序列

Question

I need to generate a sequence of numbers using C# linq. Here is how I have done it using for loop.

int startingValue = 1;
int endValue = 13;
int increment = 5;
for (int i = startingValue; i <= endValue; i += increment) {
   Console.WriteLine(i);
}

Answer 1

Try Enumerable.Range in order to emulate for loop:

int startingValue = 1;
int endValue = 13;
int increment = 5;

var result = Enumerable
  .Range(0, (endValue - startingValue) / increment + 1)
  .Select(i => startingValue + increment * i);

Console.Write(string.Join(", ", result));

Outcome:

1, 6, 11

Answer 2

If you want to mimic your procedural code, you can use TakeWhile :

 Enumerable.Range(0, int.MaxValue).
            Select(i => startValue + (i * increment)).
            TakeWhile(i => i <= endValue);

But this is to my opinion worse in terms of performance and readability.

Answer 3

Not everthing has to be done in LINQ to be usasable like Linq, you can stick very close to your original:

IEnumerable<int> CustomSequence(int startingValue = 1, int endValue = 13, int increment = 5)
{        
    for (int i = startingValue; i <= endValue; i += increment) 
    {
        yield return i;
    }
}

Call it like

var numbers = CustomSequence();

or do any further LINQ on it:

var firstTenEvenNumbers = CustomSequence().Where(n => n % 2 == 0).Take(1).ToList();

Answer 4

Seems wasteful but the best I can think of is something like this:

int startingValue = 1;
int endValue = 13;
int increment = 5;
var sequence = Enumerable.Range(startingValue,(endingValue-startingValue)+1)
               .Where(i=>i%increment == startingValue%increment);

Which is hopefully easy to follow. Logically , all of the values produced by your for loop are congruent to the startingValue modulo increment . So we just generate all of the numbers between startingValue and endingValue (inclusive) and then filter them based on that observation.