I have code in Spring Redis and put all my data in a hashmap with key value pairs. I want to be able to search every key in the hashset (not the keys containing the data) with a given prefix
So if there are 3 keys in the hashset
Cat
Car
Bar
So if I call Ca*, I want to see the values of Cat and Car.
I have been using the .scan(key, ScanOptions().match().count().build, but I have found this to be very slow. Thanks!
Related
With mapping types being removed in Elasticsearch 6.0 I wonder if IDs of documents are guaranteed to be unique across indices?
Say I have three indices, all with a "parent" field that contains an ID. Do I need to include which index the ID belongs to or can I just search through all three indices when looking for a document with the given ID?
IDs are not unique across indices.
If you want to refer to a document you need to know both the index name and the ID.
Explicit IDs
If you explicitly set the document ID when indexing, nothing prevents you from using the same ID twice for documents going in different indices.
Autogenerated IDs
If you don't set the ID when indexing, ES will generate one before storing the document.
According to the code, the ID is securely generated from a random number, the host MAC address and the current timestamp in ms. Additional work is done to ensure that the timestamp (and thus the ID sequence) increases monotonically.
To generate the same ID, when the JVM starts a specific random number has to be picked and the document ID must be generated in a specific moment with sub-millisecond precision. So while the chance exists, it's so small that I wouldn't care about it. (just like I wouldn't care about collisions when using an hash function to check file integrity)
Final note: as a code comment notes, the implementation is opaque and could change at any time, so what I wrote might not hold true in future versions.
I've got a bunch of ES documents that I'd like to put into "collections". Each document has a unique integer as an ID. Each collection also needs to have a unique integer as an ID.
I need to be able to run queries to get a list of docs in a collection, and easily add an existing doc to a collection.
What would be the most efficient and logical way of approaching this:
An index of collections, which each has an array of document IDs, or
For each document have an array of integers (or a single integer) indicating to which collections it belongs?
Thank you.
What would be the best way to add objects into my LinkedList in alphabetical order of one of the objects parameters? I have a class that takes in last name, first name, and some other stuff. I've made an object of that class and the parameters are all user submitted, and I have to store every object that's made into a LinkedList. The objects must be added to the linked list in alphabetical order according to the last name. What would be the best way to do this?
Thanks!!
You could do a binary search through your list using the “compareTo” function to find the correct index in which to insert the new value.
The binary search consists in comparing the middle element key value with a given key, in this case, your new element. If the key match you are done, that is the correct index, if it does not but the value is greater than your key value you have to do the search again with the left half of the array, on the contrary, you do the search again with the right half
When I call mydictionary.Add(key, object), can I guarantee that the object is added to the end of the dictionary in the sense that mydictionary.ElementAt(mydictionary.Count - 1) returns that object? I'm asking because I'm used to Java where HashMap doesn't have any order at all.
I'm hoping to use the ordering given by ElementAt as a way of knowing the order in which objects were added to the dictionary without using a separate data structure.
Update: Looks like ElementAt isn't going to be of any use. Is the best way to do this to use a separate data structure to store the ordering that I need?
Thanks
There is no order to a dictionary. The ElementAt method is a linq extension method that iterates over the dictionary using IEnumerable and counts the number of things, there is no relation to the order things were added.
There is a SortedDictionary, which will sort things by key, but will not keep them in the order they were added in.
If the order is really important you could always have two data structures, a list that you add the object to and a dictionary that stores the key to list index mapping. Or put a field inside your object that set from a counter as you add it to the dictionary.
I am looking for an efficient indexed persistent data structure. I typically work in .NET and am aware of FSharp's Map however that implementation and most others I am aware of only provide a single 'index', the left side of the mapping.
Basically here is the scenario
public class MyObject
public int Id { get; }
public int GroupId { get; }
public string Name { get; }
Where the Id of an object will be globally unique set of items added. GroupId may have duplicate values, and I want to be able to query for all values with a matching GroupId and within a GroupId names will be unique but may be duplicated across different GroupId's. This not a situation where I can simply create a composite key of the 3 fields as I need independent access to groups of the items based on particular field values.
I can do this, and have in the past, using dictionaries of dictionaries, which has been recommended in other posts here on STackoverflow...however, I also want the data structure to be
1) Fully Persistent and everything that means
2) efficient in memory - meaning that versions need to share as many nodes as possible
3) efficient in modifcations - I would like it to be fast
I realize that I am asking for quite a bit here but I wanted to ask to avoid even trying to re-invent the wheel if it has already been done.
Thanks
I am not sure why elsewhere, and in existing replies to your question, people recommend to imbricate existing structures. Imbricating structures (maps of maps, maps of lists, dictionaries of dictionaries, ...) only works for two indexes if one is looser than the other (two values having the same index for Index1 implies these two values have the same index for Index2), which is an unnecessary constraint.
I would use a record of maps, as many of them as you want different indexes, and I would maintain the invariant that every value that is present in a map is present in all the others in the same record. Adding a value obviously requires adding it to all maps in the record. Similarly for removal. The invariant can be made impossible to transgress from the outside through encapsulation.
If you worry that the values stored in your data structure would be duplicated, don't. Each map would only contain a pointer. They would all point to the same single representation of the value. Sharing will be as good as it already is with simple single-indexed maps.
Just as you could use a Dictionary of Dictionaries, I expect that e.g. an F# Map of Maps may be what you want, e.g.
Map<int, Map<string, MyObject> > // int is groupid, string is name
maybe? I am unclear if you also need fast access by integer id.
You might also check out Clojure's library; I don't know much about Clojure, but a range of efficient persistent data structures seems to be one of Clojure's strengths.
It seems that you are trying to apply OOP principles to your FP application.
If you think in terms of functions, what is it you are trying to do?
If you use a List, for example, you can just tell it you want to pull all the objects that have a certain group value.
If you need fast access by group you could have a Map of Lists so you can pull up all the objects in a group.
There are different data structures and many functions that work on each, but you should first think about your problem from a functional, not object-oriented, POV.