How can I iterate over two IEnumerables simultaneously in .NET 2

问题

EDIT: I split this to two questions:

Iterate over two lists ending at the shorter one
Iterate over several lists until the last element of the longest list has been reached

Assume I have two IEnumerable with many elements. Every IEnumerable has another type T.

IEnumerable<int> ints=getManyInts();
IEnumerable<string> strings=getSomeStrings();

What I want to do is to iterate over both lists, and get an item containing one int and one string for each step, until the end of the shortest list has been reached.

for(Item<int,string> item in Foo.Combine<int,string>(ints, strings))
{
    int i=item.Val1;
    string s=item.Val2;
}

You can also give me a hint how to do this in .NET 4.

回答1:

This can be done by manually doing what the for-each loop is doing internally

IEnumerable<int> ints=getManyInts();
IEnumerable<string> strings=getSomeStrings();
using (IEnumerator<int> intsEnum = ints.GetEnumerator())
using (IEnumerator<string> stringsEnum = strings.GetEnumerator())
{
    while (intsEnum.MoveNext() && stringsEnum.MoveNext())
    {
        int i = intsEnum.Current;
        string s = stringsEnum.Current;
    }
}

EDIT for longest list:

IEnumerable<int> ints=getManyInts();
IEnumerable<string> strings=getSomeStrings();
using (IEnumerator<int> intsEnum = ints.GetEnumerator())
using (IEnumerator<string> stringsEnum = strings.GetEnumerator())
{
    bool intIsValid = intsEnum.MoveNext()
    bool stringIsValid = stringsEnum.MoveNext()
    while (intIsValid || stringIsValid)
    {
        int i = default(int)
        string s = default(string)
        if(intIsValid)
        {
           i = intsEnum.Current;
           intIsValid = intsEnum.MoveNext();
        }
        if(stringIsValid)
        {
           s = stringsEnum.Current;
           stringIsValid = stringsEnum.MoveNext();
        }
        //code goes here
    }
}

回答2:

Hint for .NET 4.0:

var result = ints.Zip(strings, (i, s) => new { Key = i, Value = s });
foreach(var item in result)
{
    int key = item.Key;
    string value = item.Value;
    // Do something with the kvp
}

回答3:

As non-LINQ-apprach (.NET 2) this can be done like this top iterate until one of the enumeration is finished:

using (IEnumerator<int> intItem = GetManyInts().GetEnumerator())
using (IEnumerator<string> stringItem = GetSomeStrings().GetEnumerator()) {
  while (intItem.MoveNext() && stringItem.MoveNext()) {
    int i=intItem.Current;
    string s=stringItem.Current;
  }
}

Edit (for your new condition), to iterate with default values until the last enumeration is done:

using (IEnumerator<int> intItem = GetManyInts().GetEnumerator())
using (IEnumerator<string> stringItem = GetSomeStrings().GetEnumerator()) {
  bool hasInt;
  bool hasString;
  while ((hasInt = intItem.MoveNext()) | (hasString = stringItem.MoveNext())) {
    int i=hasInt ? intItem.Current : default(int);
    string s=hasString ? stringItem.Current : default(string);
  }
}

回答4:

Answered here: Iterate two Lists or Arrays with one ForEach statement in C#

回答5:

I'm not sure that i understand the question / context.

Would using Dictionary work for you?

internal static class Foo
    {
        internal static Dictionary<TKey, TValue> Combine<TKey, TValue>
            ( IList<TKey> keys, IList<TValue> values )
        {
            var dictionary = new Dictionary<TKey, TValue>();
            // write your own 'combination' code...
            for (int i = 0; i < keys.Count && i<values.Count; i++)
            {
                dictionary.Add(keys[i], values[i]);
            }
            return dictionary;
        }
    }

    private static void Main(string[] args)
    {
        // collection initialization and var: .NET 3.0 or higher
        var keys = new List<int> {1, 2, 3, 5, 6, 7, 8, 10, 15, 99};
        var values = new List<string> {"one", "two", "tree", "four"};

        var combinded = Foo.Combine<int, string>(keys, values);
        foreach (KeyValuePair<int, string> keyValuePair in combinded)
        {
            int key = keyValuePair.Key;
            string value = keyValuePair.Value;
        }
    }

来源：https://stackoverflow.com/questions/4888229/how-can-i-iterate-over-two-ienumerables-simultaneously-in-net-2

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ienumerable