How to iterate two list simultaneously in java shmosel. Here is the code you probably need, however, don't underestimate the power for a for-loop: // Here you need to get the max of all the List sizes to traverse all Lists int maxSize = Math. HashMaps have been observed to go into an infinite loop in production systems. length ) { aList(i) bList(i) } Assume both lists are the same size. Iterate two lists simultaneously and create another using streams. Iterating through two lists simultaneously. concat(Stream a, Stream b) method. If thread2's list is an ArrayList or LinkedList and the two threads run simultaneously, thread Given a 2D list, the task is to iterate this 2D list in Java. Furthermore, I don't think it's guaranteed that the iterator will go through in a particular order; so if you try creating a new iterator and then just skipping over the first N to get to the point you want, I wouldn't count on that to work. Each method has its situational In Java 8, we know how to get a stream of List using stream () or parrallelStream () method of Collection interface. This post quickly explains how to join two lists using streams. You could use Vector, but it tends to work out the interface is not rich enough. I want to iterate both lists simultaneously. Guava itself provides a zip() method, but you can also write your own. I am using Selenium WebDriver with Java. Iterate over two list with just one Iterate two lists simultaneously and create another using streams. I used List in the example, maybe Collection would be even better. It only makes sense if the arrays are the same length (or you use some other rule, such as iterating only to the end of the shorter array): You can chain multiple collections together using Stream. file. E. This makes your code extendable (i. The code is as below. println", so I have to iterate through the rows. flatMap(s -> s) Example: I have two maps: Map<Date, List<Journey>> journeyMap = new TreeMap<Date, List<Journey>> Map<Date, List<Job>> jobMap = new TreeMap<Date, List<Job>> I used TreeMap because that means they're sorted by date but I want to go through both maps at the same time, get the values of Journey/Job, then do some work. But if you want a solution which scales to a very long list the correct approach is to zip the two lists (or streams) together (this way you avoid looping twice), and use a function to produce the combined result. Hot Network Questions Run command on each line of CSV file, using fields in Suppose that we have two threads, one adding elements to the list and the second one reading the list's size. So the time-complexity of the whole algorithm will be linear. out. Comparing two iterators and checking which elements were added, removed or the same between the two. iterator(); // Iterating How do you iterate over two arrays of the same size, accessing the same index each iteration The Scala Way™? for ((aListItem, bListItem) <- (aList, bList)) { // do something with items } The Java way applied to Scala: for(i <- 0 until aList. . iterate simultaneously over two lists using thymeleaf. If both lists are of same size of 2 then i can procedd like . This is not a very recurring topic in Java, but sometimes it may be necessary. The main goal of this article, in particular, is to show how to create some good code designs for greater code reuse. Iterate over two list with just one Iterator Java. Only for experimenting. izip(): Python 3: Output: (‘white’, 1, 365) (‘red’, 2, 366) itertools. length) && (i < list2. To print these correspondences, you need a way to systematically iterate through multiple lists in Python. plusDays(1)) . I have to use "System. size(); assert n == listTwo. firstnames and people. 5. In this article, we will learn to iterate list in our Java application. max(list2. Combining results from both lists in a meaningful way. Instance variable names begin with small letters, so key, value1 iterating and filtering two lists using java 8. In the third case, you can only modify the list contents by removing the current element and, then, only if you do it through the remove method of the Assuming Java 8 and considering the fact that feedbackStatus may contain more than one element with the same ID. iterator(); while (aIterator. Follow edited Dec 23, 2022 at 7:36. } is, according to the Java Language Specification, identical in effect to the explicit use of an iterator with a traditional for loop. This checks for the presence of an element by putting it into an Hello! I am having with the second part of this java program - wherein you use a nested for loop to iterate as many lines as are = to the numerator. I'm reading J. In this example, we will demonstrate how to combine values from two lists into a new list by iterating over them in parallel. Using IntStream to iterate over indices of both lists simultaneously. Methods 6: Using Spliterator (Java 8 and later) Java 8 introduced the Spliterator interface, which stands for “split iterator. asked Dec 23, 2022 at 7:24. hasNext() && i2. Most efficiently. foreach method. Auxiliary Space: O(1), Constant space is used for loop variables (i in this case). charAt(i)); } Complex different-size In Java, the for-each loop is often used for iterating over arrays, but it does not natively support simultaneous iteration over multiple arrays. stream() and then iterate using Stream. Record. length)) or if you know the lists will be unmodified during iteration you could check right before the loop to see if list1 and list2 have equal lengths, in which case you can get away with not checking the bounds of both during iteration with a clear conscience. Here's the same thing in a bashier style, using a for loop. append() method and (b) list comprehension. Stream within a Stream using two list. I wonder if there's such a way to iterate thru multiple collections with the extended for each loop in java. The second list has also objects having the same attributes but the values are negatieve. You could also get a null, an ArrayOutOfBoundsException, or something left up to the implementation. The method takes two Stream instances as parameters and puts the . In this tutorial, we’ll learn a few ways to iterate through two ArrayListcollections simultaneously. Java 8 stream with two Lists. See the Looping Constructs section in the reference manual. I have to iterate first hash then second to get values. Collections class and it's static methods. Enabling parallel processing with the `. For each pair of elements, we put the key and the value into the result HashMap , def perform_func_on_each_object_in_each_of_multiple_containers(func, containers): for container in containers: for obj in container: func(obj) perform_func_on_each_object_in_each_of_multiple_containers(some_action, (deque1, deque2, deque3) and all the other arguments as your lists to iterate over. I have a List[Message] and a List[Author] which have the same number of items, and should be ordered so that at each index, the Message is from the Author. 7k 7 7 gold badges 78 78 silver badges 145 145 bronze badges. If it is, create a DummyClass object from the key and the values from both maps. In case there is a short iterator(s), this function results in a tuple as the None value. Ask Question Asked 6 years ago. The three forms of looping are nearly identical. For each iteration print the element. mybatis iterate through map When it comes to iterating through two ArrayLists simultaneously in Java, you can use the Collection#iterator method to achieve this. null elements are then filtered out and the If you have a preferred method for iterating through Maps or any other Java tips, feel free to share them in the comments below! #JavaProgramming #Maps #Iteration #CodingTips Follow Java doesn't have a way to set up an iterator that starts in the middle. I have 2 lists at hand. Once you have When it comes to iterating through two ArrayLists simultaneously in Java, you can use the Collection#iterator method to achieve this. Further, the only loop available is the #foreach loop which can iterate only over an instance of Iteratable, so we cannot use the Iterators as My ideas: Define a class for your pairs. The new element is inserted before the implicit cursor: a subsequent call to previous() would return the new element If you don't want to wait for . First is superset having list of strings and second is list of objects. Ask Question Asked 9 years, I have to iterate over user List and UserDetails List and then check if id's match and then construct the UserRepsonse Object and then add them to a list. traversing a list has O(n) complexity and since you do that for each element, your general complexity is O(n * m). asked Jan 30, 2019 at 7:33. 22. I also show how to join two lists without using streams but with the list instances. private static <T1, T2> void iterateSimultaneously(Iterable<T1> c1, Iterable<T2> c2, BiConsumer<T1, T2> consumer) { Iterator<T1> i1 = c1. Stream API simplifies parallel operations over collections. I would strongly consider adding a Comparable abstract class with two implementations (one containing a MyClass1, and the other a MyClass2). (as it makes two arrays per itteration). 0. iterator(); while (i1. 4. List<Integer> list = Arrays. At that point you can use all the normal collection framework methods to process this. 70. ) is a static factory returning a List itself, there is no need to wrap it into a ArrayList::new constructor. hasNext()) { assert bIterator. zip_longest(): It does not stop after executing the smallest element of the list. How to Hello everyone. NET 4. Using IEnumerable with foreach loop in C#. I have two list X,Y. I have a "connect four board" which I simulate with a 2d array (array[x][y] x=x coordinate, y = y coordinate). NET 2. So essentially, I have two hashmaps, one containing the following values: rId33=image23 rId32=image22 rId37=image2 And the other containing this data: {image2. 0, you could implement your own Zip method. print(a. #!/bin/bash array=( "Vietnam" "Germany" "Argentina" ) array2=( "Asia" "Europe" "America" ) for i in "${!array[@]}"; do printf "%s is in @BoratSagdiyev, Not using the old Java file APIs, but if you're on a modern JVM then the java. In the following code, the operation returns a String array consisting of the first and second element of the pair if the first element starts with "err", null otherwise. each row of the list is another list. the problem is simple, you have a List if ids in customers; for each of those ids you are traversing the tracks list to find what you need. // Creating iterators for two ArrayLists Iterator wordsIterator = words. I also have class that we'll call here SmartMessage, with a constructor taking 2 arguments: a Message and the corresponding Author. Something like that, where somefunction produces something like Stream<Pair<A,B>>. What i want is to iterate over those 2 lists and in every iteration i want to pair maximum values of the first list with the minimum values of the second and sum them. I am trying to create a method that loops through a list of WebElements to return the first WebElement that contains the text "Ooga Booga", or return null if there are no elements in the list that contains this text. Improve this question. iterator(); Iterator<C> cIterator = cList. 50. we can do this using the addAll() method of the ArrayList class. g (from an iPython I have two arrayLists ArrayList one = {A, B, C, D, E} ArrayList two = {B, D, F, G} I want to have my final ArrayList which will have All the elements of one and the You can't modify a Collection while iterating over it using an Iterator, except for Iterator. With Java 5 onwards, Iterator is used less (explicitly), because of the for-each construct, that uses Iterable and Iterator underneath. if you want to add a third field). var res = val. Is there a way of using a counter to access the object or do something similar to the for loop below ? In Python, there are several efficient ways to iterate over two lists simultaneously. next()); } } // Sometimes, we have data in multiple lists that we need to join together, connecting the first item from the first list with its counterpart in the second, and so on. List can be iterated using its forEach method that will use lambda expression as an argument. But what if we want a stream of two List or stream of List of Lists as a single logical stream to combine/merge those lists as one or do the same process on all. iterator(); Iterator<B> bIterator = bList. Complexity of the above Method: Time Complexity: O(n), where ‘n’ is the size of the list. Alternatively you could transform both sets into something like HashMap<String,HashMap<String,List<MyClassX>>>, then just How to most elegantly iterate through parallel collections? Is there an accepted Java equivalent to Python's zip()? I have to iterate simultaneously over two Collections of objects to see if their members are equal. First list has objects having 2 attributes; name (string) and an positief value (integer). Each object in this second list has one string field with which i want to In Java, using streams to iterate over two lists simultaneously allows for functional programming techniques to simplify operations. Asking for help, clarification, or responding to other answers. asList. Bloch's "Effective Java" and now I'm at the section about for-each vs for-loop. here is the code using old java: You have one list containing names, one containing ages, and one representing the schools. Follow edited Feb 1, 2019 at 8:40. If you would first create a Set of ids from customer - you would improve the efficiency, since contains in a Set has the 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). time classes: // Monday, February 29 is a leap day in 2016 (otherwise, February only has 28 days) LocalDate start = LocalDate. possible duplicate of Best way to iterate over two lists simultaneously? – skaffman. You don't really need to know what might go wrong, just don't do it. In this example, we will demonstrate how to combine values To calculate the average of two lists in Java we first need to combine the two lists into one. for (int i = 0; i < a. Transform the list into a Map using ID as key and having a list of elements. lastnames you can do: I'd like to iterate two Java-8-Streams together, so that I have in each iteration-step two arguments. [ [5, 10], [1], [20, 30, 40] ] Iterate a 2D list: There are two ways of iterating over a list of list in There is no such option in Velocity that can help us iterate multiple Collections simultaneously. Iterate in sequence over the elements of the list items1 then items2. parallel()` method. of(. size(), Math. What would be the good approach to decide to create a pool of threads? Split list into multiple To iterate over an array, slice, string, map, or channel, we can use for _, x := range []int{1, 2, 3} { // do something } How can I iterate over two slices or maps simultaneously? At the same time, I want to apply repetitive styling for that card, until map iterate through all jobs. Stream Filter of 1 list based on another list. Since you are referring to the list by its interface, you should always prefer using an Iterator as opposed to get(), because you do not know whether the latter will be equally efficient. The most common approaches utilize the built-in `zip()` function and the `itertools` module. 0. So, this article is going to show you how to get Java Stream of Multiple Lists using Java 8 Stream API (Stream interface) with an example. However, there are efficient ways to work around this limitation, notably using traditional for loops or Zip-like implementations via libraries. It seems clear that what's needed here is associations between MobileSuits and Pilots and that's exactly what a Map is for. Defining such a class is even simpler in Java 16 with the new records feature. Create an ordered list of indices: int n = listOne. The entries are expected to correspond to each other so Elizabeth is 15 years old and goes to Franklin High School. – I have a list of approximately a thousand Java objects and am iterating a List container to process them, the same processing for every object. Java - looping through LinkedhashMap and get the value. there is a possibility to have the two lists different sizes . size(), list3. Write your class as a record when it’s main purpose is communicating data, transparently and immutably. difference() utility that gives you a MapDifference instance letting you inspect exactly what is the same or different between two maps. zip_longest execute till each element of the list does not get ran. Iterate the list and use the Map to find all messages. Parallel iteration— If you need to traverse multiple collections in parallel, then you need explicit control over the iterator or index variable, so that all iterators or index variables You need to iterate over both iterators simultaneously, i. Use java. I've playing around with Generics and have a light problem here in my code. prototype. For example, if you have two lists people. printLn(X(i) +" "+Y(i)); } example result : stringX1 stringY1 stringX2 stringY2 Answers for Java, too, please. However, if you use the listIterator() method, which returns a ListIterator, and iterate over that you have more options to modify. parse("2016-03-02"); // 4 days between (end is inclusive in this example) Stream. He mentioned three cases where we couldn't use the for-each loop and one of them is the following:L. List<String> listA = new Arraylist(); List<String> listB = new Arraylist(); Given above 2 lists, I want to iterate and call the same method on each element. ; Define your Lists with the convinient method Arrays. After factoring an accuracy tolerance of +/-5%, for both of these approaches, the zip() function was found to perform faster than the enumerate() function, than using a list-index, than using a manual counter. You can use Set. You can first convert selectedList to Set and then use filter() method array of objects. Java Streams for looping twice over same list. Currently I am iterating both lists with a nested for-loop. limit(ChronoUnit. Simultaneously Iterate over multiple arrayLists in Java. The Answer by dreamcrash is correct: While your looping of a pair of arrays works, you should instead take advantage of Java as a OOP language by defining your own class. Now, use for You can mutate your List while streaming it through the following idiom. DAYS. Stream` API in Java. Shashwat Tyagi. size(); Integer[] indices = new Integer[n]; for (int i = 0; i < n; ++i) { indices[i] = i; } Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company In Java, using streams to iterate over two lists simultaneously allows for functional programming techniques to simplify operations. Another solution is to use the StreamEx library which provides a pairMap method that applies a given function to the every adjacent pair of elements of this stream. next(), i2. It is easy to understand, short and automatically generates generic collections. forEach( // for each element Same Order : Simple same-size case :. List provides methods to convert it into Iterator, ListIterator and Java 8 style, using the java. ) // do something Is there anyway to iterate two hashmaps at the same time without using two loops? Currently, I have a method that accepts two parameters and each parameter value is stored in first and second hashmap. has to check whether the id of the objects exists in the set or not. with one loop. NET Iterate through an IEnumerable several elements at a time. ” It provides a way to iterate over elements in a more parallel-friendly manner. hasNext(); assert Iterate two Lists or Arrays with one ForEach statement in C#. length(); i++) { System. asList(1,2,3); // cannot have a re-assignable index here as it requires being effectively final int[] i = {0}; // iterating list list. Stream and filter one list based on other list. A stream operation is fine. Instead, it could sit in the cache until a synchronization point where the Java memory model requires that cached writes get flushed. You can't do what you want with the foreach syntax, but you can use explicit indexing to achieve the same effect. accept(i1. concat() Method In this article, I will discuss iterating two collections simultaneously. There are many ways to iterate list. util. Which are lists of Strings . Iterate over multiple lists at a time Iterate over the entry set of map1. The following works with . Modified 6 years ago. range(0, Stack Overflow for Teams Where developers & technologists share private knowledge with coworkers; Advertising & Talent Reach devs & technologists worldwide about your product, service or employer brand; OverflowAI GenAI features for Teams; OverflowAPI Train & fine-tune LLMs; Labs The future of collective knowledge sharing; About the company Best way to test for an integer (including java. But what if we want a stream of two List or stream of List of I have 2 lists with varying length. The idea is to create a chart of remainders as output, like so: Remainders: n n%1 n%2 For 200 lines it probably doesn't make any difference what solution you choose. Note that this is absolutely horrible code, and constitutes a horrible practice altogether. 3. Iterator<A> aIterator = aList. iterate(start, date -> date. Solutions. of Stream. List. parse("2016-02-28"), end = LocalDate. In Java, one uses an Iterator when you don't want to know about the underlying Collection implementation. You will probably find that you Let’s take an example to execute zip() and itertools. Modified 5 years, I meant to replace the two lists with a Map. We’ll look at loops, iterators, streaming, and third-party utilities t In this guide, we will explore how to effectively process two lists in parallel using the `java. I'm also using printf instead of echo. between(start, end) + How to iterate two Lists or Arrays with one foreach statement in C - Set two arrays. lang. Example 1: Using the Stream. I receive jobs information from an api and styling is hardcoded. concat() The easiest way to join two lists with Streams is by using the Stream. you could write a very nice, general-purpose method for "iterating over two lists and doing something to each pair" if it did. 2D list (list of lists) The 2D list refers to a list of lists, i. Nitin D Nitin D. index to get the index of the current round of iteration, and then use it as a lookup for the second list. of and flatMap in Java 8 and iterate over sequentially in order passed to Stream. From the javadoc for add():. For each entry, check if the key is also in map2 (use the filter method of your stream). I think there must be a good way to do it but I don't know : To iterate over two HashMaps in Java simultaneously, we can use the same key set from both maps to ensure alignment. For creating lists: Two types of list creation approaches were explored: using the (a) list. Zip(str, (n, w) => new { Number = n, Word = w });The above fetches both the arrays with int and string elements respectively. . Here is a general comparison function (0 when equal, < 0 when A < B, > 0 when A > B): Java - Iterate two lists, compare then add to another list. This method enhances performance by utilizing multi In this tutorial, we covered various methods to iterate through two ArrayLists simultaneously in Java including traditional loops, iterators, and Streams. Provide details and share your research! But avoid . e. Commented Feb 21, 2012 at 9:20. This method allows us to access corresponding values based on shared keys, maintaining efficiency and clarity in our code. DirectoryStream allows you to iterate over a directory, and could be implemented to have a small memory footprint but the only way to tell for sure would be to monitor memory usage on a particular platform. stream. hasNext()) { consumer. print(b. This approach allows you to navigate through each element of both ArrayLists efficiently. I want to iterate ove the list2 and if the name2 of list2 is not null than update the name1 of list1. 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. 1. My question is how how to iterate through two Arraylists simultaneously (without Iterator) and at the same time making a "couple" by getting objects from those two arraylists in the method combine()? I've commented examples in the code also how the output should look like. ; Use superclasses or interfaces as variable types. The enhanced for loop:. This approach allows you to navigate Any better/efficient way to iterate two lists simultaneously using Java 8? java; java-8; Share. In other words, it begins with locator one - if the locator is present it returns true and exists the loop. 2. charAt(i)); System. max(list1. size())); IntStream. Both lists contain data which has to be matched with entries from the other list. In Java, using streams to iterate over two lists simultaneously allows for functional programming techniques to simplify operations. for (E element : list) { . jpeg=C:\Documents and Settings\image2. var val = new [] { 20, 40, 60}; var str = new [] { ele1, ele2, ele3};Use the zip() method to process the two arrays in parallel. Modify objects while iterating 2 Lists using java stream. So something like: for (Object element : collection1, collection2, . We can convert List into Stream by calling List. 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 I have 2 lists: List1: Object1 (name1, id1) List2: Object2(name2, id2) Given the size of list1 is the same as list2. What I want to do, is to create a List[SmartMessage], combining the From anishsane's answer and the comments therein we now know what you want. The code would be: Thanks for contributing an answer to Stack Overflow! Please be sure to answer the question. Utilizing multiple CPU cores for improved performance. 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. nio. iterator(); Iterator numbersIterator = numbers. remove(). MyBatis - Iterate over list which is value of HashMap in nested foreach loops. for (int i =0; i<anyList. Iterate over their entries simultaneously. How do I iterate through a Java Linked Hash map? 0. 13. Re: semantic purity -- you could check the list2 bounds during iteration ((i < list1. Using streams. Iterating over two arrays simultaneously using for each loop in Java. Each method has its advantages depending on your specific needs such as handling lists of different lengths, and performance considerations. of(s1, s2 ). Java 8 : Iterate from 2 lists and create a Map<String, Custom Object> Hot Network Questions Tremor Signs is an universal detection spell? What was the first SFF movie to influence later books in the same franchise? Guava provides a Maps. If you just want to iterate over the entries in two maps simultaneously, it's no different than iterating over any other Collection. Integer) in a multimethod dispatch? Best way to write a unix(y) tool with Clojure ? How to developing multiple libraries/applications simultaneously? Add support for two parameters to rand and rand-int Idiom #141 Iterate in sequence over two lists. Provide an iterator over the contents of two lists simultaneously? Ask Question Asked 14 years, 7 months ago. size(); i++){ system. The each thread will process 1 object and for 10 threads will process 10 orders simultaneously. PS Also in your DummyClass respect the Java naming conventions. I want to create a method where I iterate through a list of locators (XPath / CSS) and program chooses whichever one works. And this method has O(1) time-complexity. java; list; spring-boot; iterator; thymeleaf; Share. In Java 5, Iterator is mostly used when you want to iterate and conditionally remove elements. You are pointing the same Then, we use a while loop to iterate over both lists simultaneously, using the next() method of each Iterator to retrieve the next element in the list. iterator(); Iterator<T2> i2 = c2. – Alex D. Filtering a list of list of object with another list in Java 8. You can call varStatus. filtering a stream against items in another list. rkspqm wixdw hbsxm rqaoh ttbbc ulsurq wvc ztj rbtue vaup cgqsw oql zijm frh rcduamh