How can you compare arrays and hash tables? (2024)

Arrays are like the lockers in a school hallway - numbered storage bins lined up in a row. You can access each "locker" by its index number, store data in any locker you want, and add or remove lockers. The lockers are all the same size and shape, just like array values are the same data type. So arrays store data in an organized, numbered sequence for easy retrieval - like keeping your jackets and lunches handy in school lockers!

An array is a collection of similar data elements stored at contiguous memory locations. It is the simplest data structure where each data element can be accessed directly by only using its index number.Following are types of indexing used in ArrayZero Based Indexing- The first element of the array refers to index 0.One Based Indexing- The first element of the array refers to index 1.Following are some the advantages of using ArrayArrays represent multiple data elements of the same type using a single name.Accessing or searching an element in an array is easy by using the index number.An array can be traversed easily just by incrementing the index by 1.Arrays allocate memory in contiguous memory locations for all its data elements.

The important thing to remember is that an array has an address for its starting point and sometimes this is used to reference it or it’s first element. You can also do some pointer math. Some languages allow you to reallocate space for the array and some don’t.Using multiple arrays is another way to access data and store information about that data and you can access the data by using the same index.

Imagine you have a special box with lots of little slots in it. Each slot has a label, like a name tag. When you want to remember something, you put it in the box and attach a name tag to it. Then, if you want to find it later, you just look at the name tag to know which slot it's in. Hash tables work like this special box – they help us remember things and find them quickly by using name tags.

I much prefer these for storing data and working with data. I’ve been told you can often tell what kind of programming a person wants to perform by the kind of data structure they use and whether that is an array or a hashtable.There is no indexing with hash tables, so why bother using an array in modern programming other than to save some time?In many offices, and for many projects this is actually the question, “Why use an indexed collection of anything that doesn’t have any management features control indexing?” I think at the management level. This is a still ongoing debate and most don’t have a need to solve for this question.Proofs for anything are hard for most people.

Arrays have a fixed size, but in C & C++ we use malloc to create new pointer and copy from the old value this will ensure the size change smoothly. Hash table use for a specific case, so to get specific order and have dynamic size there are alternative like Vector.

A hash table is like a dictionary, where you can look up a definition (object or value) by the word that represents it. It could be any value, and doesn't need to be words, however.Some languages do support for duplicate values per key in hash tables (unordered_multimap in C++), so this is not entirely correct.

In summary, arrays are great for situations where you have a fixed sequence of elements and need fast index-based access, while hash tables are better when you have key-value pairs and need efficient lookups, insertions, and deletions based on keys.

In addition to chaining and linear probing, there are other collision resolution techniques that can be used with hash tables such as quadratic probing and double hashing. These techniques can help improve the performance of hash tables when dealing with collisions.

Hash table performance was hit by collision, due to collision we need to traverse through linked list to find the value for the given. The new implementation has been improved now, for example after JDK 8 Java use binary tree instead of linked list. This make lookup faster

Hash table storage size differ in different language. This is mainly based on when the language runtime decides to increase the size and what is the rate at which this grows in memory. Most of the run time grows at 2x level except C++ and C# (both of them grow more than 2x)

Accessing elements in an array is fast and constant time (O(1)) because you can directly access an element using its index.Accessing elements in a hash table is generally fast and constant time (O(1)) on average. However, it can degrade to O(n) in the worst case if there are hash collisions (two keys map to the same bucket).

I'll typically use a hash table (or dictionaries) when I want fast lookup based on a unique key, and don't care about the order of items.Arrays when order matters, or when I know the number of items in advance, and when I need to iterate over items in sequence. It's worth noting that searching for elements requires O(n) in worst-case.

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I think this boils down to considerations of both performance and algorithm. Ignore memory differences for now, since that is largely implementation specific. When you have key value pairs and need to access them in random or unordered ways, a hash table is probably the right choice. When you have a set of values with no key, that are accessed as a set or iterated through, maybe an array is the right choice. Some alternatives like dictionaries or associative arrays could land in the middle of these two choices and might not be implemented in the same way that a hash table would be, so the performance expected might not be there, but access characteristics should be largely maintained. A lot of this will come down to implementation.

There are many kinds of data structures tob consider. Breadth Search and Depth Search trees, Hash Maps, etc. There are also multiple ways to implement them to avoid key collisions. So there is no single structure that is best for every situation. This why we also develop metrics for every new algorithm so we can make correct choices

On the whole, I think it is better to conceptualize the array as a base type of data structure, and build upon that with hash table concepts. If someone is learning about the difference between them, this approach builds a better mental model.Later, adding information about the differences between hash tables and dictionaries or associative arrays can help further clarify the underlying mechanics of these structures.Language specific implementations are important. For example, a dictionary in some language might leverage keys and values but not have the performance of a hash table due to the algorithms it leverages. An associative array might be similar to a dictionary, or it might not. These variations need concrete examples and metrics.

How about programming languages? Also about speed of development and urgency of requirements?Memory and speed of data retrieval?Size of data?