Nesting loop to get one of each

Question

I'm trying to make a look to print each of every value once:

Something like this.

Lets pretend that the object letters contains "one,two ...ten"

And then there is the object numbers that contains "1,2,3,4...10"

Now if I want the loop to print:

One 
1 
Two
2 
Three
3

How would the loop look like?

I tried it like this:

     foreach (var i in letters)
{
       Console.WriteLine(i);

     foreach(var a in numbers)
        {
            Console.WriteLine(a);
        }
}

But this returns:

One 
1
2
Two
1
2
Three
1
2

And that result isn't what I want..

How can I nest the loops to make it print the way I want it?

Duplicate: http://stackoverflow.com/questions/1955766/iterate-two-lists-or-arrays-with-one-foreach-statement-in-c-sharp — Marcio Bueno, Apr 07 '16 at 14:29
@Simon.S This has been open for a long while. If one of these answers solved your issue, please accept it to make it more visible for those looking for a similar answer. — David Watts, Jun 26 '17 at 14:44

score 6 · Answer 1 · answered Apr 07 '16 at 14:29

6

Maybe you can use IEnumerable<T>.Zip(...), see here, to make combinations.

var data = letters.Zip(numbers, (l, n) => new { letter = l, number = n})
foreach (var item in data) {
    Console.Writeline(item.letter);
    Console.Writeline(item.number);
}

answered Apr 07 '16 at 14:29

Maarten

22,527
3
47
68

score 3 · Answer 2 · answered Apr 07 '16 at 14:29

3

use forloop insted of foreach use it like this

for (int i=0;i<letters.length;i++)
{
  Console.WriteLine(letters[i]);
  Console.WriteLine(numbers[i]);
}

answered Apr 07 '16 at 14:29

rashfmnb

9,959
4
33
44

Beat me to it. Nested loops aren't necessary in this case. – levelonehuman Apr 07 '16 at 14:29
2

in case `letters.Count` == `numbers.Count` - otherwise `i < Math.Min(letters.Count,numbers.Count )` – fubo Apr 07 '16 at 14:34

score 3 · Answer 3 · answered Apr 07 '16 at 14:30

Don't do two nested loops, they are for enumerating over all possible pairs from two collections.

Instead, make a loop on the index, and use it for both collections, or use LINQ's Zip method:

foreach (var pair in letters.Zip(numbers, (l, n) => new {Letter=l, Number=n})) {
    Console.WriteLine("{0} - {1}", pair.Letter, pair.Number);
}

score 2 · Answer 4 · answered Apr 07 '16 at 14:33

2

Assuming your Numbers and Letters are collections that derive from IEnumerable, you could do something like this:

 var zipped = letters.Zip(numbers, Tuple.Create);

 foreach (var tuple in zipped)
 {
     Console.WriteLine(tuple.Item1);
     Console.WriteLine(tuple.Item2);
 }

answered Apr 07 '16 at 14:33

David Watts

2,249
22
33

Is it possible to loop more than two values using this method? – Simon.S Apr 11 '16 at 07:45
Yeah it is possible. If all of your collections are the same length, you zip the first pair, then zip the results of the next pair, but it would be a bit untidy as you would end up with nested tuples @Simon.S – David Watts Apr 11 '16 at 09:23

score 1 · Answer 5 · answered Apr 07 '16 at 14:29

You need a single loop to iterate over both lists:

for (int index = 0; index < letters.Count; index++)
{
    Console.WriteLine(letters[index]);
    Console.WriteLine(numbers[index]);
}

This presupposes that your lists are the same length. If they're not you'd have to set the upper limit to the length of the shorter list.

for (int index = 0; index < Math.Min(letters.Count, numbers.Count); index++)

score 0 · Answer 6 · answered Apr 07 '16 at 14:29

You're close - the second loop should not be within the first, but you should use one loop to iterate over both arrays. Try:

for (int i = 0; i < letters.size(); i++) {
 Console.WriteLine(letters.getItem(i));
 Console.WriteLine(numbers.getItem(i));
}

Note that this assumes a size() method to return the number of items and a getItem() method to return a specific item from the object.

score 0 · Answer 7 · answered Apr 07 '16 at 14:43

What's happening is that for every time your outside loop runs, the inside one runs twice.

That's because your loops are nested, there's no getting around this. If you absolutely must use nested loops for this, you'd have to add a check whether your number has been printed yet

Something like:

foreach(var i in letters)
{
    Console.WriteLine(i);

    foreach(var a in numbers)
    {
        if (a.isPrinted) //if it has been printed already
        {
            continue; //skip ahead
        }
        else
        {
            Console.WriteLine(a.number);
            a.isPrinted = true;
            break; //stop and jump out of the foreach loop
        }
    }
}

This also means that each number is actually an object that holds the bool isPrinted and int number
I wouldn't doing it like that, it's ridiculously inefficient.
You should do what others have already suggested.

Nesting loop to get one of each

7 Answers7