Retrieving an Element of an Array: Difference between revisions

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{{task}}
{{DeprecatedTask}}

'''Please do not add new code, and merge existing code to the [[Arrays]] task.'''


In this task, the goal is to retrieve an element of an [[array]].
In this task, the goal is to retrieve an element of an [[array]].

==[[4D]]==
[[Category:4D]]

` first element
$elem:=$array{1}

==[[X86 assembly]]==
[[Category:x86 assembly]]

'''Assembler:''' nasm
mov esi, array_offset
mov ebx, 2
mov eax, [esi+ebx*4]

==[[ActionScript]]==
[[Category:ActionScript]]
var arr:Array = new Array(1,2,3);
var myVar:Number = arr[1];
// the value of myVar is: 2

==[[Ada]]==
[[Category:Ada]]
Array indexed by an enumerated type. Ada enumerated types are discrete non-numeric types.
type Days is (Mon, Tue, Wed, Thu, Fri, Sat, Sun);
type Daily_Counts is array(Days) of Natural;
This_week : Daily_Counts := (200, 212, 175 220, 201, 120, 0);
Monday_Sales : Natural;

Monday_Sales := This_Week(Mon);
Monday_Sales is assigned 200

==[[AppleScript]]==
[[Category:AppleScript]]
on getArrayValue(array, location)
-- very important -- The list index starts at 1 not 0
return item location in array
end getArrayValue

==[[C]]==
[[Category:C]]
int array_index(int array[], int index) {
return array[index];
}

==[[C sharp|C#]]==
[[Category:C sharp]]

int getArrayValue( int values[], int index ) {
return values[index];
}

==[[C plus plus|C++]]==
[[Category:C plus plus]]

template<typename T>
T array_index(T array[], size_t index) {
return array[index];
}

==[[ColdFusion]]==
[[Category:ColdFusion]]
<cfset arr = ArrayNew(1)>
<cfset arr[1] = "one">
<cfset arr[2] = "2">
<cfset arr[3] = 3>
<cfset var = arr[1]>
The value of '''var''' is "one"

''ColdFusion Arrays are '''NOT''' zero-based, their index begins at '''1'''''

==[[Common Lisp]]==
[[Category:Common Lisp]]

(defun array-value (array index)
(aref array index))

==[[Delphi]]/[[Object Pascal]]/[[Turbo Pascal]]/Standard [[Pascal]]==
[[Category:Pascal]]

Array's in all the flavors of pascal can be of any valid base type, or user defined type ( which are all made up of base types ) and are multi-dimensional. With Delphi dynamic arrays were defined but had been used in pascal since its inseption.

A Static array defintion:
foo : array[1..10] of integer; { The base index is ONE }
The base index can be freely chosen:
foo: array[7 .. 16] of integer; { The base index is 7 }
Indeed, the "1 .. 10" resp. "7 .. 16" are actually ''types'': they are integer subrange types. Arrays can also be indexed by enumeration types or enumeration subrange types:
type
rainbowcolor = (red, orange, yellow, green, blue, violet);
var
foo: array[rainbowcolor] of integer;
bar: array[yellow .. blue] of integer;
i: integer
begin
i := foo[red]; { allowed indices are red, orange, yellow, green, blue, violet }
i := bar[green]; { allowed indices are yellow, green, blue }
end;
A Dynamic Array type in Delphi:
foo : array of integer ; // The base index is ZERO
An "old school" dynamic array in the various flavors of pascal
foo : array[0..0] of integer; // The base index is ZERO
A dynamic array in Extended Pascal:
type
intarray(n: integer) = array[1 .. n] of integer; { base index 1 }
var
foo: ^intarray;
begin
new(foo, 10); { foo now has index 1 to 10 }
i := foo[2];
dispose(foo); { get rid of the array }
end;
In the case of the static array, the compiler generates the code to allocate the required memory to hold 10 integers.

In the Delphi style ---dynamic--- array you must set its length:
SetLength(foo,10); // this array will no hold 10 integers
In the "old school" style of dynamic arrays, you created a point to the zero length declaration and then allocated memory to it with GetMem
pFoo : ^Foo ;
Foo : array[0..0] of integer ;

All arrays are accessed the same way regardless of declaration method.

i : integer ;
i := foo[n] ;
where n is the array index who's base is either 1 or 0 depending on how it was declared.

==[[Erlang]]==
[[Category:Erlang]]

Erlang lists are 1-based which means that the index must be within the bounds (1 .. length(List)):

Value = lists:nth(Index, List).

==[[Forth]]==
[[Category:Forth]]
Forth does not have special syntax for array access. Address arithmetic is used to access contiguous memory.
create array 1 , 2 , 3 , 4 ,
array 2 cells + @ . \ 3

==[[Groovy]]==
[[Category:Groovy]]

Define an array
arr = ['groovy', 'is', 'a', 'great', 'language']

First element
arr[0] // *** 'groovy'

Last element, negative indexes
arr[-1] // *** 'language'

Ranges
arr[-3..-1] // *** ['a', 'great', 'language']

Mix n Match
arr[0..2, -1] // *** ['groovy', 'is', 'a', 'language']

==[[IDL]]==
[[Category:IDL]]

; this is allowed:
result = arr(5)
; but this is preferred:
result = arr[5]

The form with square brackets is preferred as it unambiguously constitutes array access, while the version with round ones can conflict with a function call if there are both a function and an array with the same name <tt>arr</tt>.

==[[Java]]==
[[Category:Java]]

public Object getArrayElem(Object[] array, int pos) {
return array[pos];
}

==[[JavaScript]]==
[[Category:JavaScript]]

var element = array[index];

==[[MAXScript]]==
[[Category:MAXScript]]
item = arr[index]

==[[mIRC]]==
[[Category:mIRC Scripting Language]]

'''Interpeter:''' mIRC Script Editor

'''Library:''' [[mArray Snippet]]

[[Category:mArray Snippet]]

alias readmyarray { echo -a $array_read(MyArray, 2, 3) }

==[[Perl]]==
[[Category:Perl]]

'''Interpreter:''' [[Perl]] 5.8.8
$elem = $array[0];

==[[PHP]]==
[[Category:PHP]]

$array = array('php', 'has', 'arrays');
// First element
$elem = $array[0];

==[[Pop11]]==
[[Category:Pop11]]

lvars ar = {1 two 'three'};
lvars elem;
;;; Access second element and assign to variable elem
ar(2) -> elem;

This example uses the simplest possible array (a vector). Pop11 has
more general arrays, but in all cases access follows the same pattern,
and look the same as procedure (function) call.

==[[Python]]==
[[Category:Python]]

'''Interpreter:''' Python 2.5

The item is an element in a list at a given index
item = aList[index]

or

To use a list like a stack be it FIFO/LIFO
aList.pop() # Pop last item in a list
aList.pop(0) # Pop first item in a list
'''Note:''' When using the pop() method, the element is removed from the list.

==[[Ruby]]==
[[Category:Ruby]]

ary = ['Ruby','rules','big','time']
#the first element
element = ary[0]
#or
element = ary.first
# => element = 'Ruby'

#the last element
element = ary[-1]
#or
element = ary.last
# => element = 'time'

#retrieving different values at once
elements = ary.values_at(0,2,3)
# => elements = ['Ruby','big','time']

#select the first element of length 3
element = ary.find{|el|el.length==3}
# => element = "big"

==[[Smalltalk]]==
[[Category:Smalltalk]]

#($a $b $c) at: 2

==[[Tcl]]==
[[Category:Tcl]]

All arrays in Tcl are associative. If "key" is the variable that holds the key of the element to be retrieved, then

set result $array($key)

==[[Toka]]==
[[Category:Toka]]

This retrieves the value 20 from the second item in the array:

3 cells is-array table
( Populate the array )
10 0 table array.put
20 1 table array.put
30 2 table array.put
table 1 array.get

Latest revision as of 15:06, 29 November 2019

Retrieving an Element of an Array was a programming task. It has been deprecated for reasons that are discussed in its talk page.

Please do not add new code, and merge existing code to the Arrays task.

In this task, the goal is to retrieve an element of an array.

Retrieved from "https://rosettacode.org/wiki/Retrieving_an_Element_of_an_Array?oldid=6526"