Iterate through multiple collections in the same "for" loop?

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I wonder if there's such a way to iterate thru multiple collections with the extended for each loop in java.

So something like:

for (Object element : collection1, collection2, ....)
         // do something ...

Thanks

You can do exactly this with Guava's Iterables.concat():

for (Foo element : Iterables.concat(collection1, collection2)) {
    foo.frob();
}

Iterating through multiple collections at the same, Iterating through multiple collections at the same time. Hello, I'm currently trying to develop a workflow that tracks data sheets and emails� Re: Iterating through multiple collections at the same time Hi, I had exactly the same issue - i created an iteration through the list item ID and then a filtered query list in the loop setting two variables with the list fields I need for further processing.

Collection<Foo> collection1 = ...
Collection<Foo> collection2 = ...
Collection<Foo> collection3 = ...
...

Collection<Foo> all = ...
all.addAll(collection1);
all.addAll(collection2);
all.addAll(collection3);
...

for(Foo element : all)
{

}

How to iterate through multiple collections in Scala, What is the Idiomatic way of iterate through multiple collections in call zipped along with any collection you want to iterate at the same time:. Iterate through multiple collections at once in scala. Now, what is the idiomatic way of doing it in scala?.In my case I needed to iterate through the collection and also have the index of the current item being iterated, this can be achieved with the method zipWithIndex, then call zipped along with any collection you want to iterate at the same time:

If your lists have the same length, just use the raw for loop:

Object[] aNum = {1, 2}; 
Object[] aStr = {"1", "2"}; 

for (int i = 0; i < aNum.length; i++) {
    doSomeThing(aNum[i]);
    doSomeThing(aStr[i]);
}

It works!

How To Iterate Over Two (or More) Lists at the Same Time, If you have had multiple data sets that needed to be jointly computed or displayed, then you probably have experienced the pain of iterating� Python Iterate over multiple lists simultaneously Iterating over single lists, refers to using for loops for iteration over a single element of a single list at a particular step whereas in iterating over multiple lists simultaneously, we refer using for loops for iteration over a single element of multiple lists at a particular step.

With plain Java 8 and without any additional libraries:

public static <T> Iterable<T> compositeIterable(Collection<? extends T>... collections)
{
    Stream<T> compositeStream = Stream.of(collections).flatMap(c-> c.stream());
    return compositeStream::iterator;
}

Then you can use it as:

for (Foo element : MyClass.compositeIterable(collection1, collection2)) {
    foo.frob();
}

The 4 Methods for Iterating Collections in Java, Java concepts and code example for collection iteration. Or you may want to traverse through a list of numbers in order to calculate the sum This code snippet does the same thing as the classic for loop example above. There are a lot of ways to do specific things with multiple containers as provided in the algorithm header. For instance, in the example you've given, you could use std::copy instead of an explicit for loop. On the other hand, there isn't any built-in way to generically iterate multiple containers other than a normal for loop.

Java, A quick and practical guide to combining multiple collections in Java. The static method concat() combines two Streams logically by creating a lazily creates a new collection with additional references to the same objects that are in the first two collections: Iterator<? extends E> listIterator = i1.iterator();. You can create a new thread and iterate your list there. Spawn multiple of this therad and you can iterate your list in parallel. If you want to pass List of any template type, you can just specify your method parameter as List, although this might result in compiler warnings.

The For-Each Loop, The For-Each Loop. Iterating over a collection is uglier than it needs to be. Finally, it is not usable for loops that must iterate over multiple collections in parallel. Say I have 2 parallel collections, eg: a list of people's names in a List<String> and a list of their age in a List<Int> in the same order (so that any given index in each collection refers to the same person). I want to iterate through both collections at the same time and fetch the name and age of each person and do something with it.

Looping through (foreach) multiple collections?, Usually, I access my collections using @foreach($dogs as $dog) {{ $dog-> name }} @endforeach Is multiple collections? Posted 4 years ago by CuddlyHammy In my case they're of the same length. If not, maybe I� If you don't want to wait for .NET 4.0, you could implement your own Zip method. The following works with .NET 2.0. You can adjust the implementation depending on how you want to handle the case where the two enumerations (or lists) have different lengths; this one continues to the end of the longer enumeration, returning the default values for missing items from the shorter enumeration.

Comments
  • What is the semantics of that? All of collection1, then collection2? Or first of all collections, then second of all collections...
  • @user1291492 That is a syntax error, of course. So it would have to be "something different".
  • Right, that obviously doesn't work. But I'm just wondering if there're some "nice" ways to do the similar things without actually changing the original collections.
  • It is surprising that Java does not provide a CompositeCollection, or something like this.
  • @Raedwald it pretty much does, with Streams.
  • This's doing a copy. (which is not what I'd like because that'd increase memory usage)