PHP Learning Array Courseware Page 1/2_PHP Tutorial

Subscript: The identification name in the array, which is the code name of the string or integer in the array

The number of index values ​​​​in the array is called a several-dimensional array.
Index value: An index is a structure that sorts the values ​​of one or more columns in a database table.

Array classification
Arrays in PHP are divided into two types:
Indexed array: Indexed (indexed) index value is an integer, starting with 0. Indexed array is used when identifying things by position.
Associative array: Associative (associative) association uses a string as the index value, the index value is the column name, and is used to access the column data.

Arrays are usually assigned by assignment
Generally, there are two ways of assigning arrays:
$a[1]="dsadsadsa";
$b[2]="dsadsadsad" ;
Use the array function:
$a=array("dsads","dsadsa",321312);
One-dimensional array: When there is only one index value (subscript) of the array, it is called one dimensional array.
Format of direct array assignment:
$Array variable name [index value] = data content;
Note: The index value can be a string or an integer, but 1 and "1" are different, they are the same One is an integer and one is a string.

Arrays with the same name without index values ​​are arranged in order.
Example:
$a=array(1,2,3,4,5,6);
$b=array("one", "two", " three");
$c=array(0=>"aaa",1=>"bbb",2=>"ccc");
$d=array("aaa",6 =>"bbb","ccc");
$e=array("name"=>"zhang", "age"=>20);
?>
Two-dimensional Array
Format of multi-dimensional array:
$a[0][]="dsadas";
$a[0][]="dsadsa"; This group is under the 0 index value under $a 1 and 2
If the array function is used to declare the format as follows:
$a=array("dsadsa","dsadas",21,array("dsadsa","dsadas"));

Array traversal
foreach loop structure:
foreach only uses array loops in two formats
foreach(array_exprssion(array expression) as $value);
foreach(array_exprssion(array expression) as $key=>$value);
The first format traverses the given array_exprssion array. Each time through the loop the current value is assigned to my $calue and the pointer inside the array moves forward one step.
The second format does the same thing, except that the key value of the current cell will also be assigned to the variable $key in each loop.
When foreach starts executing, the pointer inside the array will automatically point to the first unit. Also note that foreach operates on a copy of the specified array, not the array itself
$arr=array(10,20,30,40,50,60);
foreach($arr as $k= >$v){
echo "$k=>$v
";
}

Output result: 0=>10 1=>20 2=> 30 3=>40 4=>50 5=>60//Subscript=>integer
Combined use of list(), each() and while loop
each():
$ arr=array(1,2,3,4,5);
$a=each($arr);
print_r($a);
Output result: Array ( [1] => 1 [value] => 1 [0] => 0 [key] => 0 )
Get the first value of the array value subscript key
list():
$arr3 =array("a","b","c");
list($key,$value)=each($arr3);

echo $key."
" .$value;
Output result: 0 a List() can be said to assign a value to a set of variables in one step. It can only be used for numerically indexed arrays and assumes that the numerical index starts from 0.
while loop
$arr=array(1,2,3,4,5,6,7,8,9,);
while(list($key,$value)=each($ arr)){
$key++;
echo $key."=>".$value;
echo "
";
}
echo "
";
Output result: 1=>1 2=>2 3=>3 4=>4 5=>5 6=>6 7=>7 8=>8 9= >9
reset() array pointer redirection
After executing each(), the array pointer will stay at the next unit in the array or at the last unit when the end of the array is reached.
is_array detects whether the variable is an array true and returns true false false
$arr=array(1,2,3,4,5,6,"saas");
while(list($k,$ v) = each($arr))
{
if(is_array($arr))
{
$x += $v;
echo $x;
}
else
{
$x += $k;
}
}
This example cannot fully reflect the function of is_array, but it can be used as a reference.
Array pointer
next(): responsible for moving the pointer backward
prve(): responsible for moving the pointer forward
end(): will point the pointer to the last element of the array
reset(): Unconditionally move the current pointer to the first index position
Syntax format: mixed next (array name)
$arr=(array(1,2,3,4,5));
echo end($arr);
Output result: 5
Key(), current() and count()
The function of key() is to read the index value of the data pointed to by the current pointer.
The current() function reads the content data of the data pointed to by the current pointer.
The count() function is used to count the number of all elements in the array, which means that the function will return the length value of the target array.
Format: int count (array name);

key(): Get the key name from the associative array
$array = array('fruit1' => 'apple','fruit2' => 'orange','fruit3' => 'grape','fruit4' => 'apple','fruit5' => 'apple');
while ($fruit_name = current($array )) {
if ($fruit_name == 'apple') {
echo key($array).'
';
}
next($array);
}
Output results: fruit1, fruit4, fruit5

current(): Return the current unit in the array
$transport = array('foot', 'bike', 'car', 'plane');
$mode = current($transport); // $mode = 'foot';
$mode = next($transport); // $mode = 'bike';
$mode = current($transport); // $mode = 'bike';
$mode = prev($transport); // $mode = 'foot';
$mode = end($transport) ;       // $mode = 'plane';
$mode = current($transport); // $mode = 'plane';
Pay attention to the example to return the current unit in the array

count (): Calculate the number of units in the array
$arr=array(1,2,3,4,5,6);
echo count($arr);
Output result: 6

array_change_key_case()
array_change_key_case returns an array whose string key names are all lowercase or uppercase
The morphological functions included are two [CASE_UPPER] converted to uppercase, [CAS_LOWER] converted to lowercase.
$input_array = array("FirSt" => 1, "SecOnd" => 4);
print_r(array_change_key_case($input_array, CASE_UPPER));
Output result: Array ([FIRST] => 1 [SECOND] => 4 )

array_chunk()
array_chunk() function will decompose the data content of the target array into several small arrays based on the specified number of indexes. in the original array.
$arr=array(1,2,3,4,5,6);
$a=array_chunk($arr,3);
print_r($a);
Output result: Array ( [0] => Array ( [0] => 1 [1] => 2 [2] => 3 ) [1] => Array ( [0] => 4 [1] => 5 [2] => 6 ) )
It is equal to dividing the sum of the number of array units by 3

array_count_values ​​
array_count_values ​​is used to calculate the occurrence of each value in the target array Count
Syntax format: array_count_values ​​(target array)
The result value returned by this function will be expressed in the form of an array using the content data of the original array as an index.
$arr=array(1,2,3,3,2,6);
print_r(array_count_values($arr));
Output result: Array ( [1] => 1 [2 ] => 2 [3] => 2 [6] => 1 )

http://www.bkjia.com/PHPjc/319094.htmlwww.bkjia.comtruehttp: //www.bkjia.com/PHPjc/319094.htmlTechArticleSubscript: The identification name in the array is also a string or integer. How many codes are there in the array? The index value is called a dimensional array. Index value: The index is a column in the database table or...