Questions tagged [arrays]

An array is an ordered linear data structure consisting of a collection of elements (values, variables, or references), each identified by one or more indexes. When asking about specific variants of arrays, use these related tags instead: [vector], [arraylist], [matrix]. When using this tag, in a question that is specific to a programming language, tag the question with the programming language being used.

An array is an ordered linear data structure consisting of a collection of elements (values or variables), each identified by at least one index, stored in contiguous memory locations.

An array is typically stored so that the position of each element can be computed from its index tuple by a mathematical formula.

In some languages (C, Java, etc.) the length of the array must be set beforehand. In other languages (Ruby, Python, LISP, Haxe, etc.) the length of the array grows dynamically as elements are added.

When tagging a question with this tag, also tag the question with the programming language being used.

Array in specific languages

  • C# arrays are actually objects and not just addressable regions of contiguous memory as in C and C++. Array is the abstract base type of all array types. You can use the properties and other class members of the Array base type.
  • C arrays act to store related data under a single variable name with an index, also known as a subscript. They are stored in row-major order, which means the last subscript varies fastest. It is easiest to think of an array as simply a list or ordered grouping for variables of the same type. As such, arrays often help a programmer organize collections of data efficiently and intuitively.
  • C++ inherits raw arrays from C and adds its own array-class std::array for compile-time array sizes, std::vector for runtime dynamic sized arrays. It also has smart pointer implementations like std::unique_ptr, std::shared_ptr.
  • Objective C inherits raw arrays from C and adds its own array-class NSArray and NSMutableArray for dynamic arrays.
  • Ruby's normal array class is called array.
  • In Python, the normal array datatype is called a list, while the array type is used for homogeneous arrays.
  • In NumPy there is a powerful N-dimensional array with many capabilities.
  • PHP arrays are implemented as ordered maps which may contain a mix of numeric or string keys.
  • JavaScript arrays are just objects with a different prototype (with additional functions more useful for array-like structures), with numerical index values stored as strings (all JavaScript keys are strings). Unlike other objects, you cannot use dot notation to access keys - only square bracket notation.
  • In Haxe, an Array has one type parameter which corresponds to the type of collection of elements. Arrays can be created using their constructor new Array() or [1, 2, 3], but also using Array comprehension: [for (i in 0...10) if (i % 2 == 0) i]. For storage of fixed size the abstract type haxe.ds.Vector can be used, which may be faster than Array on some targets and is never slower.
  • In Scala, the normal array class is called Array. To get an element from an array you use parentheses (most languages use square brackets).
  • In Java, an array is a container object that holds a fixed number of values of a single type. The length of an array is established when the array is created. After creation, its length is fixed.
  • In Perl, array variables are denoted with the @ prefix and arrays are declared with parentheses. Replacing the prefix with $# returns the last index.
  • In Rust, arrays are groups of data of the same type that are contiguous in memory, so they can be used when communicating with C. The length of an array is fixed.
  • In Swift, an array that includes the specified values, automatically inferring the array’s Element type. Swift makes it easy to create arrays in your code using an array literal: simply surround a comma-separated list of values with square brackets.
  • In Pascal, arrays declarations specify the index range rather than the number of elements; so parray: array [1..25] of real; declares a one-based array of 25 real numbers (valid elements are parray[1] thru parray[25]), whereas parray: array [0..24] of real; declares a zero-based ('C-style') array of the same size (the first element is parray[0]). Pascal array index ranges can include negative numbers!


Elements of an array are usually specified with a 0-first index, for example, myarray[0] would represent the first element of myarray. myarray[n] (where n is the length of the array minus 1) would represent the last element in the array. However, some languages such as old Fortran and Lua use 1 as the initial index.

Some languages (C++, Java, C#) have "basic arrays" and collections. Basic arrays are supported by the compiler directly, have a fixed size, and only provide element access by index. Collections, like Java's ArrayList, are system library classes implemented on the top of these basic arrays and have a wide range of various methods. In such cases, the tag should be used to name the simple arrays.

Arrays can be statically allocated or dynamically allocated. The way in which you access the array and its type varies based on how it is declared and allocated.

Arrays can contain multiple indices. For example, an array with one index (e.g. array[0]) is known as a one-dimensional array. If it has two indices (e.g. array[0][0]) it is considered two dimensional and maybe visualized as a grid. Multidimensional arrays, or, in other words, arrays with multiple indices are called matrices, or a matrix is singular.


Related tags

Where talking about specific variants of arrays, use these related tags instead:

414766 questions
150 answers

How can I remove a specific item from an array in JavaScript?

How do I remove a specific value from an array? Something like: array.remove(value); Constraints: I have to use core JavaScript. Frameworks are not allowed.
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Loop (for each) over an array in JavaScript

How can I loop through all the entries in an array using JavaScript?
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How do I check if an array includes a value in JavaScript?

What is the most concise and efficient way to find out if a JavaScript array contains a value? This is the only way I know to do it: function contains(a, obj) { for (var i = 0; i < a.length; i++) { if (a[i] === obj) { return…
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How to insert an item into an array at a specific index?

I am looking for a JavaScript array insert method, in the style of: arr.insert(index, item) Preferably in jQuery, but any JavaScript implementation will do at this point.
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Create ArrayList from array

Given an array of type Element[]: Element[] array = {new Element(1), new Element(2), new Element(3)}; How do I convert this array into an object of type ArrayList? ArrayList arrayList = ???;
Ron Tuffin
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Sort array of objects by string property value

I have an array of JavaScript objects: var objs = [ { first_nom: 'Lazslo', last_nom: 'Jamf' }, { first_nom: 'Pig', last_nom: 'Bodine' }, { first_nom: 'Pirate', last_nom: 'Prentice' } ]; How can I sort them by the value of…
Tyrone Slothrop
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Checking if a key exists in a JavaScript object?

How do I check if a particular key exists in a JavaScript object or array? If a key doesn't exist, and I try to access it, will it return false? Or throw an error?
Adam Ernst
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46 answers

Loop through an array in JavaScript

In Java, you can use a for loop to traverse objects in an array as follows: String[] myStringArray = {"Hello", "World"}; for (String s : myStringArray) { // Do something } Can I do the same in JavaScript?
Mark Szymanski
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How can I check if an object is an array?

I'm trying to write a function that either accepts a list of strings, or a single string. If it's a string, then I want to convert it to an array with just the one item so I can loop over it without fear of an error. So how do I check if the…
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Deleting an element from an array in PHP

Is there an easy way to delete an element from an array using PHP, such that foreach ($array) no longer includes that element? I thought that setting it to null would do it, but apparently it does not work.
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How to append something to an array?

How do I append an object (such as a string or number) to an array in JavaScript?
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Get all unique values in a JavaScript array (remove duplicates)

I have an array of numbers that I need to make sure are unique. I found the code snippet below on the internet and it works great until the array has a zero in it. I found this other script here on Stack Overflow that looks almost exactly like it,…
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How do I determine whether an array contains a particular value in Java?

I have a String[] with values like so: public static final String[] VALUES = new String[] {"AB","BC","CD","AE"}; Given String s, is there a good way of testing whether VALUES contains s?
Mike Sickler
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How do I declare and initialize an array in Java?

How do I declare and initialize an array in Java?
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What's the simplest way to print a Java array?

In Java, arrays don't override toString(), so if you try to print one directly, you get the className + '@' + the hex of the hashCode of the array, as defined by Object.toString(): int[] intArray = new int[] {1, 2, 3, 4,…
Alex Spurling
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