Consider the following pseudo Map<String, Set<String>>: What is the best way to join the value Sets into a single Set (above example should be [“A”, “B”, “C”, “D”]). The order of the resulting set does not matter. I know that I can to something like this: But it feels kind of ugly and I’m wondering if there is a better
Tag: dictionary
Java Collectors Grouping By
I have an input of integers and I would like to sort all even numbers before all odd ones in ascending order and preserve the odds order. I am pretty sure I can achieve that with collectors and/or downstream collectors, but I am not sure how to do it. I would like to know how can I sort the false
Report on a multimap by producing a new map of each key mapped to the count of elements in its collection value
Imagine a multimap tracking persons, each of whom has a list of assigned tasks. How can I use streams to get a new map, mapping each Person to an Integer with the count of items found in their list of assigned tasks? How to get a result equivalent to this hard-coded map: I have been trying permutations of: Answer You
How to create a dictionary in java [closed]
Closed. This question needs debugging details. It is not currently accepting answers. Edit the question to include desired behavior, a specific problem or error, and the shortest code necessary to reproduce the problem. This will help others answer the question. Closed 2 years ago. Improve this question Can i get some help on creating a dictionary in java? I tried
java.util.Map values() method performance
I have a map like this with several million entries: I need to get list of values, which could be done by calling java.util.Map values() method. Is Collection of values created every time I call values() method or is it pre-computed from performance perspective? As my Map has several millions elements, I do not want to create new list object
Java Determine If String Starts With Key In Map
I want to determine if a given String startsWith any key in a Map. The simple solution is to iterate through entire the keySet. My question is: Is there is a better data structure to handle this problem? Answer This can’t be done directly with an HashMap: the problem is that HashMap uses an hash calculated on the key to
How to sort data in a CSV file using a particular field in Java?
I want to read a CSV file in Java and sort it using a particular column. My CSV file looks like this: Considering I want to sort it using the third column, my output should look like: After some research on what data structure to use to hold the data of CSV, people here suggested to use Map data structure
Memory map for Neo4j embedded
When using Neo4j in the embedded mode (Java API), one can manually set memory map settings using the following API calls (or similar): My question is: Is the mapped memory allocated out of Java heap/extended memory or from the rest of the memory available. I know that for Neo4j server the latter is correct as long as it is run
Convert a JSON String to a HashMap
I’m using Java, and I have a String which is JSON: Then my Map in Java: I want to store all the data from the JSONObject in that HashMap. Can anyone provide code for this? I want to use the org.json library. Answer In recursive way: Using Jackson library:
How do I use the new computeIfAbsent function?
I very much want to use Map.computeIfAbsent but it has been too long since lambdas in undergrad. Almost directly from the docs: it gives an example of the old way to do things: And the new way: But in their example, I think I’m not quite “getting it.” How would I transform the code to use the new lambda way