PHP learning array courseware

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: The indexed index value is an integer, starting with 0. Indexed arrays are 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 usually use assignment
Generally, there are two ways to assign arrays:
$a[1]="dsadsadsa";
$b[2]="dsadsadsad";
Use the array function:
$a= array("dsads","dsadsa",321312);
One-dimensional array: When the array has only one index value (subscript), it is called a 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. One of them belongs to an integer and the other to 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 = & gt; "aaa", 1 = & gt; "bbb", 2 = & gt; "ccc");
$ d = array ("aaa", 6 = & gt; "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 1 and 2 under the 0 index value under $a
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 two formats: array loop
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
Combining 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 values ​​to a set of variables in one step. It can only be used for numerically indexed arrays and assumes numerical indexing Start from 0 .
while loop
$arr=array(1,2,3,4,5,6,7,8,9,);
while(list($key,$value)=each($arr)){
$ key++;
                                                     $key."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 It 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()
key() function 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 result: fruit1, fruit4, fruit5

current(): return array The current unit in
$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 value in the array Unit

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
It contains two morphological functions [CASE_UPPER] to convert to uppercase, and [CAS_LOWER] to convert 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() sub-function will decompose the data content of the target array into several small arrays with the specified number of indexes and include them 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 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 )

array_fill
array_fill allows users to customize values ​​to fill the specified index section in the target array.
Syntax format: array_fill (starting index position, section size, specified character)
The starting index position and section size must be integer (integer) values, and the section size specified must not be 0.
$a = array_fill(5, 6, 'banana');
print_r($a);
Output result: Array([5] => banana[6] => banana[7] => banana[ 8] => banana[9] => banana[10] => banana)

array_filter
array_filter passes each value in the target array to the user-defined function in turn. If the user-defined function returns TRUE (true
), the current value of the input array will be included in the returned result array. The key names of the array remain unchanged.
Syntax format: array_filter (target array, user-defined function)
function odd($var)
{
return($var % 2 == 1);
}
$array1 = array("a"=> 1, "b"=>2, "c"=>3, "d"=>4, "e"=>5);
print_r(array_filter($array1, "odd"));
Output result: Odd:Array([a] => 1[c] => 3[e] => 5)
$entry = array(0 => 'foo',1 => false,2 => -1,3 => null,4 => '');
print_r(array_filter($entry));
Output result Array([0] =>foo[2] => -1 )
Other callback functions: array_walk (), array_map()

array_flip
array_flip inverts the index and content value in the target array. The inverted array will use the original content value as the index, and the index As data content.
array_flip syntax format: exchange keys and values ​​in the array
array_flip (target array)
$trans = array("a" => 1, "b" => 1, "c" => 2);
$trans = array_flip($trans);
print_r($trans);
Output content: Array([1] =>b[2] =>c)
If the same value appears multiple times , the last key name will be used as its value, and all others are lost.

​ array_sum
array_sum is used to calculate the sum of all element values ​​in the array.
Syntax format: array_sum (target array)

array_unique
array_unique is used to remove duplicate data in the target array and return new values ​​after operation.

​ array_keys and array_values ​​
array_keys This function will ignore the original key name and re-index the array using sequential numbers, for associative arrays.
array_values ​​This function returns a key array containing numbers or strings. Returns all values ​​in the input array and numerically indexes them.
$arr=array("a"=>1,"b"=>2,"abc",2);
$b=array_keys($arr);
$c=array_values($arr);
Output result: $b=Array ([0] => a [1] => b [2] => 0 [3] => 1 )
$c=Array ( [0] => 1 [1] => 2 [2] => abc [3] => 2)

Retrieval of array
Retrieval of array mainly refers to judging the key name or element value of the array to determine a certain The presence or absence of array elements.
Grammar format: bool in_array(mixed $needle, array $haystack[, bool $strict]);
$arr3=array(1,2,3,"hello","wprld");
$b=in_array(" hell",$arr3,true);
var_dump($b);
$arr4=array(1,2,3,array("hello","world"));
$b=in_array(array("hello ","world"),$arr4);
var_dump($b);
Output result: bool(false) bool(true)

Conversion between arrays and variables
extract() and compact() functions perform array and Convert between variables.
After conversion, the key name of the array element and the variable name, as well as the value of the element and the value of the variable maintain a corresponding relationship.
extract This function is used to pour variables from the array into the current symbol table
$info = array("user_id"=>2006001,"user_name"=>"Tong Xiangyu", "position"=>"Project Manager ");
extract($info);
echo $user_id;
Output result: 2006001
compact() accepts a variable number of parameters. Each parameter can be a string containing a variable name or an array containing a variable name. The array can also contain other arrays whose unit contents are variable names. compact() can be processed recursively.
$city = "San Francisco";
$state = "CA";
$event = "SIGGRAPH";
$location_vars = array("city","state");
$result = compact("event", "nothing_here",$location_vars);
print_r($result);
Output result: Array ( [event] => SIGGRAPH [city] => San Francisco [state] => CA )

Array and stack
The array_push() function pushes one or more elements onto the end of the array stack (push) and returns the number of elements pushed onto the stack. The
array_pop() function pops the last element of the array stack and returns the element.
Example array_push
$a=array("dsa","dsas","dfs","gfd");
array_push($a,"ssss","ddddd");
print_r($a);
Output Result: Array ( [0] => dsa [1] => dsas [2] => dfs [3] => gfd [4] => ssss [5] => ddddd )
Example array_pop Pops and returns the last element of array and decrements the length of array by one. If array is empty (or not an array) NULL will be returned.
$a=array("dsa","dsas","dfs","gfd");
array_pop($a);
print_r($a);
Output result: Array ( [0] => dsa [1] => dsas [2] => dfs )

Arrays and Columns
A queue can also appear in the form of an array. The first element in the array is the head, and the last element is the tail.
You can use the stack method to insert elements at the end of the pair.
To delete the opposite element from the queue array, you can use the array_shift function, which shifts the first element of the array out and returns it as the result. At the same time, the length of the array is reduced by 1, and other elements are moved forward one bit. All numeric key names will be changed to count from zero, and text key names will not change.
array_shift example
$a=array("dsa","dsas","dfs","gfd");
$title=array_shift($a);
print_r($a);
Output result: Array ( [ 0] => dsas [1] => dfs [2] => gfd )
You can use the array_unshift() function to insert one or more elements at the beginning of the queue array. This function returns the number of successfully inserted elements.
$a=array("dsa","dsas","dfs","gfd");
$title=array_unshift($a,"a",array(1,2));
print_r($a) ;
Output result: Array ( [0] => a [1] => Array ( [0] => 1 [1] => 2 ) [2] => dsa [3] => dsas [4] => dfs [5] => gfd )
It can be seen from the results that you can also insert the array

Sorting of the array
Ignore the array sorting of the key name
sort() positive
rsort() inverted
usort ()
$arr = array("3"=>"lemon", "2"=>"orange", "4"=>"banana", "1"=>"apple");
ksort($arr);
foreach ($arr as $key => $val) {
“echo “$key = $valn”;
}

Calculation of Array
Calculations on arrays are more convenient. The simplest calculation is to find the sum of all elements inside an array. You can also treat arrays as a set, merge two or more arrays, calculate the difference or intersection between arrays, etc.
Merge of arrays Merge is not +
Example
$arr2=array(1,2,3);
$arr3=array(3,4,5);
$a=array_merge($arr2,$arr3);
print_r($a);
Output result: Array ([0] => 1 [1] => 2 [2] => 3 [3] => 3 [4] => 4 [5] => 5)
Calculate the difference set of arrays
$array1 = array("a" => "green", "red", "blue", "red");
$array2 = array("b" = > "green", "yellow", "red");
$result = array_diff($array1, $array2);
print_r($result);
Output result: Array ([1] => blue) Difference The level is to take the previous difference value
to calculate the intersection of the arrays
$array1 = array("a" => "green", "red", "blue");
$array2 = array("b" => " green", "yellow", "red");
$result = array_intersect($array1, $array2);
print_r($result);
Output result: Array ( [a] => green [0] => ; red ) The intersection takes the

common to both upper and lower sides to create an array of the specified range:
range();
Remove duplicate values ​​in the array:
array_unique();
Return the array in reverse order:
array_reverse();

Random function of array: Random number
srand((float) microtime()*10000000) Set the random generator seed
array_rand();
array_shuffle();
Example
echo date("Ymd").rand(1000000,9999999 )."jpg";

Output result: 200805096246795jpg's random number

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