Sort notes for commonly used array operations in PHP

PHP has a traditional array structure and is constantly improved with version upgrades. for example, PHP 5.4 can use short array definition syntax, which we will discuss in this article, next, let's take a look at the notes on the commonly used array operation methods in PHP: Overview
To access the content of a variable, you can directly use its name. If the variable is an array, you can use a combination of variable names and keywords or indexes to access its content.
Like other variables, you can use operator = to change the content of array elements. Array units can be accessed using the array [key] syntax.

Basic operations on arrays
Php defined array:

<?php   $array = array();   $array["key"] = "values"; ?> 

There are two ways to declare arrays in PHP:

1. use the array () function to declare an array,
2. assign values directly to array elements.

<? Php // array $ users = array ('phone ', 'computer', 'dos ', 'Linux'); echo $ users; // only the data type Array print_r ($ users) is printed ); // Array ([0] => phone [1] => computer [2] => dos [3] => linux) $ numbers = range (1, 5 ); // create an array print_r ($ numbers) that contains the specified range ); // Array ([0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5) print_r (true ); // 1 var_dump (false); // bool (false) // print_r can print the string and number simply. the Array starts with Array and is expressed as a key value, print_r outputs Boolean values and null results without significance, so it is more appropriate to use var_dump // display all values in the array through loops for ($ I = 0; $ I <5; $ I ++) {echo $ users [$ I]; echo'
';} // Count the number of units in the array or the number of attributes in the object through count/sizeof for ($ I = 0; $ I <count ($ users); $ I ++) {echo $ users [$ I]; echo'
';} // You can use the foreach loop to traverse the array. the advantage is that you do not need to consider key foreach ($ users as $ value) {echo $ value .'
'; // The point number is the string connection symbol} // foreach looping $ key => $ value; $ key and $ value are variable names, you can set foreach ($ users as $ key => $ value) {echo $ key.'
'; // Output key}?>

Create an array of custom keys

<? Php // create an array of custom keys $ ceo = array ('apple' => 'jobs', 'Microsoft '=> 'Nadella', 'Larry page ', 'Eric '); // if the key of the element is not declared, it will start from scratch print_r ($ ceo ); // Array ([apple] => jobs [microsoft] => Nadella [0] => Larry Page [1] => Eric) echo $ ceo ['apple']; // jobs // usage starting from php5.4 $ array = ["foo" => "bar", "bar" => "foo",]; print_r ($ array ); // Array ([foo] => bar [bar] => foo)?>

From php5.4, you can use the short array definition syntax and replace array () (). It is somewhat similar to the array definition in javascript.

Use of each ()

<? Php // create an array by assigning values to the array element $ ages ['trigger4'] = 22; echo $ ages .'
'; // Array // because the index of the related Array is not a number, you cannot traverse through the for loop. you can only use the foreach loop or list () and each () structure // use of each // each returns the current key/value pair in the array and moves the array pointer one step forward $ users = array ('triggerkit4' => 22, 'Mike '=> 20, 'John' => 30); // print_r (each ($ users )); // Array ([1] => 22 [value] => 22 [0] => trigkit4 [key] => trigkit4) // equivalent: $ a = array ([0] => trigkit4, [1] => 22, [value] => 22, [key] => trigkit4 ); $ a = each ($ users); // each wraps the first element of the original array into a new array and assigns it to $ a echo $ a [0]; // tri Gkit4 //!! Convert existing data to a Boolean value echo !! Each ($ users); // 1?>

The each pointer points to the first key-value pair, returns the first array element, obtains its key-value pair, and wraps it into a new array.

Use of list ()
The list is used to assign the values of the array to some variables. the following example shows the result:

<? Php $ a = ['2', 'ABC', 'Def ']; list ($ var1, $ var2) = $ a; echo $ var1 .'
'; // 2 echo $ var2; // abc $ a = ['name' => 'trigkit4', 'age' => 22, '0' => 'boys']; // list only lists the indexes whose key is a number ($ var1, $ var2) = $ a; echo $ var1; // boy?>

Note: list only recognizes the index with the key as a number.

Sorting of array elements
Reverse sorting: sort (), asort (), and ksort () are both positive sorting, and of course there is a corresponding reverse sorting.
Implementation reversely: rsort (), arsort (), and krsort ().

The array_unshift () function adds new elements to the array header. the array_push () function adds each new element to the end of the array.
Array_shift () deletes the first element in the array header. the opposite function is array_pop (). It deletes and returns an element at the end of the array.
Array_rand () returns one or more keys in the array.

The shuffle () function sorts array elements randomly.
The array_reverse () function provides a reverse sorting of the original array.
Use of APIs for arrays
Count () and sizeof () count the number of objects under the array
Array_count_values (): number of lower-level values in a group

<? Php $ numbers = array ('20140901', '2'); sort ($ numbers, SORT_STRING); // sort by string, the string is only the first size print_r ($ numbers ); // Array ([0] => 100 [1] => 2) $ arr = array ('trigkit4', 'banner ', '10'); sort ($ arr, SORT_STRING); print_r ($ arr); // Array ([0] => 10 [1] => banner [2] => trigkit4) shuffle ($ arr ); print_r ($ arr); // random sorting $ array = array ('A', 'B', 'C', 'D', '0', '1 '); array_reverse ($ array); print_r ($ array); // reverse sorting of the original array. Array ([0] => a [1] => B [2] => c [3] => d [4] => 0 [5] => 1) // Copy the array $ arr1 = array ('10', 2); $ arr2 = & $ arr1; $ arr2 [] = 4; // $ arr2 is changed, $ arr1 is still array ('10', 3) print_r ($ arr2 ); // Array ([0] => 10 [1] => 2 [2] => 4) // Use of asort $ arr3 = & $ arr1; // currently, arr1 and arr3 are the same $ arr3 [] = '3'; asort ($ arr3); // sorts the array and retains the original relationship print_r ($ arr3 ); // Array ([1] => 2 [2] => 3 [0] => 10) // Use of ksort $ fruits = array ('C '=> 'Bana', 'a' => 'apple', 'D' => 'Orange'); ksort ($ fruits); print_r ($ fruits ); // Array ([a] => apple [c] => banana [d] => orange) // use array_unshift for unshift ($ array, 'z '); // add an element print_r ($ array) at the beginning ); // Array ([0] => z [1] => a [2] => B [3] => c [4] => d [5] => 0 [6] => 1) // use echo current ($ array) for current (pos); // z; obtain the current unit in the current array // use echo next ($ array) for next ); // a; move the internal pointer in the array one forward. // use echo reset ($ array ); // Z; point the internal pointer of the array to the first unit // use echo next ($ array) for prev; // a; echo prev ($ array ); // z; returns the echo sizeof ($ array); // 7; counts the number of array elements // array_count_values $ num = array (10, 20, 30, 10, 20, 1,); // counts the number of occurrences of the array element print_r (array_count_values ($ num )); // Array ([10] => 3 [20] => 2 [30] => 1 [1] => 1 [0] => 1)?>

Current (): each array has an internal pointer pointing to its current unit, initially pointing to the first element inserted into the array

For loop traversal

<?php  $value = range(0,120,10);  for($i=0;$i
 

Array instance
Use of the array_pad function

<? Php // array_pad function, which can be appended at the beginning and end of an array $ num = array (1 => 10, 2 => 20, 3 => 30); $ num = array_pad ($ num ); print_r ($ num); // Array ([0] => 10 [1] => 20 [2] => 30 [3] => 40) $ num = array_pad ($ num,-5, 50); // array_pad (array, size, value) print_r ($ num ); // Array ([0] => 50 [1] => 10 [2] => 20 [3] => 30 [4] => 40)?>

Size: the specified length. An integer is filled to the right, and a negative number is filled to the left.

Use of unset ()

<? Php // unset () use $ num = array_fill (, rand (); // rand (min, max) print_r ($ num ); // Array ([0] => 8 [1] => 8 [2] => 8 [3] => 8 [4] => 8) echo'
'; Unset ($ num [3]); print_r ($ num ); // Array ([0] => 8 [1] => 8 [2] => 8 [4] => 8)?>

Use of array_fill ()

<? Php // Use of array_fill () $ num = range ('A', 'E'); $ arrayFilled = array_fill (, $ num); // array_fill (start, number, value) echo'
';  print_r($arrayFilled);?>
Use of array_combine ()
<?PHP  $number = array(1,2,3,4,5);  $array = array("I","Am","A","PHP","er");  $newArray = array_combine($number,$array);  print_r($newArray);//Array ( [1] => I [2] => Am [3] => A [4] => PHP [5] => er ) ?> 
Array_splice () deletes an array member.
<? Php $ color = array ("red", "green", "blue", "yellow"); count ($ color); // Get 4 array_splice ($ color, 1, 1); // delete the second element print_r (count ($ color); // 3 echo $ color [2]; // yellow echo $ color [1]; // blue?>
Array_unique: delete duplicate values in the array
<?php  $color=array("red", "green", "blue", "yellow","blue","green");  $result = array_unique($color);  print_r($result);//Array ( [0] => red [1] => green [2] => blue [3] => yellow ) ?> 
Array_flip () swap the key value and value of the array
<?PHP  $array = array("red","blue","red","Black");  print_r($array);  echo "
";  $array = array_flip($array);//  print_r($array);//Array ( [red] => 2 [blue] => 1 [Black] => 3 ) ?> 
Array_search ()
  <? Php $ array = array ("red", "blue", "red", "Black"); $ result = array_search ("red", $ array) // array_search (value, array, strict) if ($ result = NULL) {echo "no value red";} else {echo "value $ result "; // the value 0}?>