Questions tagged [dictionaries]
The dictionaries tag has no usage guidance.
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Why is sparsity useful in dictionary learning?
What is the particular reason for which we use sparse matrix X in dictionary learning equation Y=DX where Y is the signal matrix, D is dictionary and X is the coefficient matrix?
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0answers
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If statement not capturing the conditional I'm seeking [closed]
I'm working on a hw assignment, and my if statement isn't working the way it's intended.
This is an ATM machine project. I've already gotten the program to read the csv file and stored it into a ...
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1answer
36 views
Parallel Algorithm for Data Averaging
I am trying to write an efficient Parallelised algorithm for Data Averaging. By this I mean I have a list of tuples (K, V1, V2, V3) and in the end, I want a dictionary mapping K to the average of all ...
2
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1answer
89 views
Remove duplicates from dictionary in a safe and clever way
I have a dictionary that has keys and multiple values per key. Same value can be assigned to multiple keys.
For the sake of simplicity, the keys are ints and the ...
5
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1answer
139 views
Most space-efficient lossy dictionary?
Short version: What is the most space-efficient lossy dictionary (with given false positive and false negative rates)?
Long version: A lossy dictionary is a data structure $D$ that encodes a set $S$ ...
1
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1answer
62 views
Determining possible data structures given a set of required operations
This was an interview question that I was told is supposed to be an open ended discussion of the trade-offs.
You have a collection of comparable objects and want to be able to do the following:
1. ...
0
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1answer
283 views
How to read off the set represented by a van-Emde-Boas tree?
I'm reviewing my background in Algorithms and DS design. Specifically I never went through the van Emde Boas Tree. Though I can undestand the proto-vEB with related picture. I'm struggling to ...
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0answers
51 views
Dictionary matching problem: dictionary size estimation
Suppose we solve dictionary matching problem for $d$ patterns with the Aho-Corasick algorithm. Then our main data structure consists of a trie with $n$ vertices and auxiliary structures. I want to ...
2
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3answers
641 views
time efficient key value store for fast lookup
Let's state a collection of key/values.
Key is an unsigned integer (0 - 2^32-1). Hense there are comparable.
Value is few bytes fixed size.
There are 4M items in the collection.
Keys are not evenly ...
2
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1answer
338 views
Algorithms to correct misspelled word?
At present, I am doing a project on Optical Character Recognition (OCR). I am looking forward to improve the results by checking the output words of my OCR code with existing words from a text file. ...
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3answers
342 views
Match dictionary to misspelled word, corner cases
I'm trying to think of corner-cases where I can skip having to linear-search through my dictionary in my problem; For a given word w1, find all matches with the least editing distance from it in the ...
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3answers
1k views
Memoization without array
In Cormen et al.'s Introduction to algorithms, section 15.3 Elements of dynamic programming explains memoization as follow:
A memoized recursive algorithm maintains an entry in a table for the ...
6
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1answer
313 views
Best data structure for a queue with random reads?
Well, it's not exactly a queue if it allows for random reads. This question is about a data structure which behaves like a queue for insertions and a sorted dictionary for reads.
Imagine an algorithm ...
0
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1answer
236 views
What happens internally when you remove an object from a treemap
I am wondering what happens if you remove an object in the middle of a treemap.
If the treemap would look something like this:
So what would happen if you remove the number 30? Because 27 and 34 ...
4
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2answers
241 views
Fastest static associative map
Let's say that I wanted to build a key to value associative map where the only requirement was that lookup times were fast.
Once built, the associative map would not allow inserts, deletes, or ...
0
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1answer
308 views
Complexity of testing membership in a disjoint set
I have a disjoint set data structure (sometimes known as a union-find data structure) where I store a value in each "node". I want to look up a node by value. How can I do this?
The representations ...
6
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1answer
710 views
Suggest a data-structure that supports the following operations with time complexity of $ O(log(n)) $
Iv'e been struggling a lot with this one.
I am looking for a data-structure (could be a modification of an existing type of data-structure, or a combination of more than one data-structure), which ...
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3answers
140 views
Data structure choice for a query-update-delete problem
Given is an initial set of n keys. Each key k is of the form (p, q). Note that both p and q are positive.
At any given point, there are two possible actions:
1) Query-Delete: Given a value s as ...
1
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1answer
134 views
Which in-memory data structure can accommodate billions of md5 value?
For my application, I have to store billions of md5 values, and before storing new md5 I wanna make sure that it doesn't exist already in it.
I tried using hash data structure, it worked well but no ...
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2answers
669 views
O(1) access into an array-like data structure with numerical ranges for keys
Preface: It's been a long time since I've been in school, and my terminology is probably all wrong. Apologies...
Summary: I have a data structure with probability ranges assigned to the elements, and ...
1
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2answers
4k views
Data structure with constant time operations
I need to use a data structure, implementable in C++, that can do basic operations, such as lookup, insertion and deletion, in constant time. I, however, also need to be able to find the maximum value ...
2
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1answer
102 views
How can a set offer better search performance than an array
While reading the following tutorial on iOS development Working with Foundation (section on Sets near the bottom), I came across the following statement: "Because sets don’t maintain order, they offer ...
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3answers
11k views
What is the advantage of seperate chaining over open addressing?
Hash tables resolve collisions through two mechanisms,
separate chaining or open hashing and
open addressing or closed hashing.
Though the first method uses lists (or other fancier data structure) ...
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1answer
197 views
Is it possible to implement a dictionary with efficient access according to insertion order?
I am trying to build a generic data structure that needs to hold keys and values and in the same time keep track on the indices in which keys and values were put in, like arraylists do but in a ...
1
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1answer
487 views
A many-to-many mapping data structure
What would be a good way representing:
i. Given a key, return all the data values associated with that key
AND
ii. Given a data value, return all the keys that are associated with that data.
So far, ...
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1answer
3k views
Segment trees with insertion/deletion
I have a range query problem to solve. This problem requires not only range queries and update, but also insert or delete an element of the array. There is a series of operations that must be done in ...
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0answers
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Why can't fractional cascading be used on two unrelated arrays?
According to both Wikipedia and my professor (see question 5.1), fractional cascading has to be done on arrays with related data.
The specific question:
A fellow student wants to compactly store ...
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4answers
10k views
Why are Red-Black trees so popular?
It seems that everywhere I look, data structures are being implemented using red-black trees (std::set in C++, SortedDictionary ...
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1answer
540 views
Applications of queues [closed]
Let suppose a simple (FIFO) queue, where elements enter at a side and exit at the other side.
I know the classical use of queues in everyday life and computer networking. I would like to know more ...
2
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3answers
43 views
Existence of functions that only tests memberships without revealing any information about the members
Given a set of strings $\{s_1, s_2, \cdots, s_n\}$, is there a way to encode them to a program $P$, such that given some string,$s$, the program can test the membership efficiently (deterministically ...
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1answer
363 views
Find K-th next element in O(log n) time
We want to store a set S of distinct positive integers and support the following operations on S:
Insert(a): insert integer a !∈ S into S.
Delete(a): delete integer a ∈ S from S.
...
0
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1answer
1k views
Selection problem on the union of two ordered dictionaries
Suppose we are given two ordered dictionaries S and T each with n items, and that S and T are implemented by means of array-based ordered sequences. Describe an O(log n) time algorithm for finding the ...
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1answer
400 views
Data structure for range-value-sum
I have to be able to perform insert, delete, range-value-sum, and range-2-max-values with a data structure.
Range-value-sum(xl,xr): with a range [xl,xr] (for a range query), it reports the sum of ...
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2answers
729 views
Data structure to insert, update and sort indexes by frequency and query an index for a particular cumulative frequency
Here is the description of the data structure I am looking for:
Initial Original Data
Index | Frequency |
1 3
2 1
3 7
4 2
5 6
Now it should be kept ...
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1answer
1k views
Are dictionaries and associative arrays the same thing?
With respect to abstract datatypes (ADTs), are the terms "dictionary" and "associative array" perfect synonyms or are there slight differences between them?
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2answers
351 views
Term for binary search tree using hashes?
I was looking for a way to easily store and access a symbol table using the least memory and code as possible and I went with a BST. Symbols, however, tend to be defined in order as in foo0, foo1, ...
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2answers
941 views
How are hash tables O(1) taking into account hashing speed?
Hash tables are said to be amortized $\Theta(1)$ using say simple chaining and doubling at a certain capacity.
However, this assumes the lengths of the elements are constant. Computing the hash of an ...
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2answers
2k views
Tree data structure for fast merges [closed]
I need trees that have the following properties:
Each node in the tree has two values associated with it - a key and an associated opaque data element.
An internal node in the tree has unbounded ...
2
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1answer
161 views
Bloom filter variant
I've been playing around with a simple probabilistic data structure which is very similar to a Bloom filter. Where a Bloom filter would use $k$ independent hash functions to choose $k$ of the $m$ bits ...
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5answers
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Is there an anti-Bloom filter?
A Bloom filter makes it possible to efficiently keep track of whether various values have already been encountered during processing. When there are many data items then a Bloom filter can result in ...
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2answers
316 views
Why should leaf nodes in a red-black tree be black?
From the property of Red-Black Trees we know that:
All leaves (NIL) are black. (All leaves are same color as the root.)(Comren et al "Introduction to Algorithms")
But what is the reason that we ...
2
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1answer
991 views
What is a suitable data structure in this scenario?
I need an efficient data structure for maintaining a set of values.
Here, $n_1$ is the number of insertions per unit time; $n_2$ is the number of deletions per unit time; $k$ is the number of searches ...
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2answers
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Looking for a set implementation with small memory footprint
I am looking for implementation of the set data type. That is, we have to
maintain a dynamic subset $S$ (of size $n$) from the universe $U = \{0, 1, 2, 3, \dots , u – 1\}$ of size $u$ with
operations ...
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1answer
1k views
Deleting in Bloom Filters
I know that standard Bloom Filters only have operations like inserting elements and checking if an element belongs to filter, but are also some modification of Bloom filters which enable a delete ...
2
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2answers
1k views
Data structure for maintaining large space-efficient filtered array
How does one implement a space efficient data structure that satisfies the requirements below?
You have a large array
You have a filter which tells you which elements in that large array are to be ...
4
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3answers
385 views
Why do Bloom filters work?
Let's say I am using Bloom filters to create a function to check if a word exists in a document or not. If I pick a hash function to fill out a bit bucket for all words in my document. Then if for a ...
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2answers
969 views
Bloom filter and perfect hashing
A Bloom filter uses a hash function to test membership in a given set $S$, by checking if an item is present of not at the specified position.
To mitigate the effect of hash collision, multiple ...
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7answers
38k views
Are degree and order the same thing when referring to a B-Tree
I know the term order of a B-tree. Recently I heard a new term: B tree with minimum degree of 2.
We know that the degree is related to a node but what is the degree of a tree?
Does degree impose ...
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5answers
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For what kind of data are hash table operations O(1)?
From the answers to (When) is hash table lookup O(1)?, I gather that hash tables have $O(1)$ worst-case behavior, at least amortized, when the data satisfies certain statistical conditions, and there ...
