What is the difference between php hash and array

In PHP, hashes and arrays are common data types. However, there are several fundamental differences between hashes and arrays.

1. Data structure

An array is a linear data structure that can organize data through an ordered set of elements. Elements can be numbers, strings, identifiers, etc. We can use arrays to store a set of data and then access them through key-value pairs.

Hash is a non-linear data structure that consists of a set of key-value pairs. Each key-value pair is an entry. Hash tables typically use a hash operation on the key and then use the hash value as an index to access the entry. This can make the data more evenly distributed in the hash table and improve access efficiency.

2. Storage method

Arrays usually use continuous memory space to store data. For example, if we create an array of length 5, PHP will allocate a continuous memory space for it, usually 5 consecutive memory units.

Hashes usually use hash tables to store data. A hash table is a data structure consisting of a specified number of buckets. Each bucket is an element that can store one or more hash values. Hash tables store and retrieve data by hashing keys into specific buckets.

3. Efficiency

When accessing any element in the array, PHP will obtain the value of the element from memory based on the index value. This is a constant-level operation, so it is highly efficient.

However, when we use a hash table to access an entry, PHP needs to hash the key into the bucket first and then get the value from the bucket. Therefore, when the hash table accesses data, the hash table needs to consume more time and memory resources.

4. Data type restrictions

In PHP, arrays can contain any type of data, including integers, floating point numbers, strings, objects, and even other arrays. This means that various types of data can be stored in arrays and accessed through key-value pairs.

Hash is usually used to store key-value pairs. Keys must be hashable, while values ​​can be any type of data. Since the key needs to be hashed, it must be immutable, because if the key changes, the corresponding hash value will also change, which will cause the hash table to be unable to correctly locate the data.

To sum up, although both arrays and hashes can be used to store data, their storage methods, efficiency and data type restrictions are different. Therefore, when using them, we need to choose according to the actual situation. If the data types you need to store are relatively simple and you need to access them quickly, you can use arrays; if you need to store key-value pairs and you need to look them up based on the keys, you can use a hash table.

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