Detailed explanation of commonly used array operation methods in PHP

PHP has a traditional array array structure, and it is constantly improving with version upgrades. For example, from php5.4 onwards, you can use short array definition syntax, which we will talk about in this article. Let’s take a look at what is commonly used in PHP. Notes on array operation methods:

OverviewTo access the contents of a variable, you can use its name directly. If the variable is an array, its contents can be accessed using a combination of the variable name and a keyword or index.
Like other variables, the contents of array elements can be changed using operator =. Array cells can be accessed via the array[key] syntax.

Basic operations of arrays
php defines arrays:

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

There are two main ways to declare arrays in PHP :

1. Use the array() function to declare the array,
2. Directly assign values ​​to the array elements.

<?php
  //array数组
  $users = array(&#39;phone&#39;,&#39;computer&#39;,&#39;dos&#39;,&#39;linux&#39;);
  echo $users;//只会打印出数据类型Array
  print_r($users);//Array ( [0] => phone [1] => computer [2] => dos [3] => linux )

  $numbers = range(1,5);//创建一个包含指定范围的数组
  print_r($numbers);//Array ( [0] => 1 [1] => 2 [2] => 3 [3] => 4 [4] => 5 )
  print_r(true);//1
  var_dump(false);//bool(false)

//print_r可以把字符串和数字简单地打印出来，数组会以Array开头并已键值形式表示，print_r输出布尔值和null的结果没有意义，因此用var_dump更合适

//通过循环来显示数组里所有的值
  for($i = 0 ;$i < 5;$i++){
    echo $users[$i];
    echo &#39;<br/>&#39;;
  }

//通过count/sizeof统计数组中单元数目或对象中的属性个数

  for($i = 0; $i < count($users);$i++){
    echo $users[$i];
    echo &#39;<br/>&#39;;
  }
//还可以通过foreach循环来遍历数组，这种好处在于不需要考虑key
  foreach($users as $value){
    echo $value.&#39;<br/>&#39;;//点号为字符串连接符号
  }
//foreach循环遍历 $key => $value；$key和$value是变量名，可以自行设置
  foreach($users as $key => $value){
    echo $key.&#39;<br/>&#39;;//输出键
  }
?>

Create an array of custom keys

<?php

  //创建自定义键的数组
  $ceo = array(&#39;apple&#39;=>&#39;jobs&#39;,&#39;microsoft&#39;=>&#39;Nadella&#39;,&#39;Larry Page&#39;,&#39;Eric&#39;);
  //如果不去声明元素的key,它会从零开始
  print_r($ceo);//Array ( [apple] => jobs [microsoft] => Nadella [0] => Larry Page [1] => Eric )

  echo $ceo[&#39;apple&#39;];//jobs

   //php5.4起的用法
  $array = [
    "foo" => "bar",
    "bar" => "foo",
  ];

  print_r($array);//Array ( [foo] => bar [bar] => foo ) 

?>

From php5.4 onwards, you can use short array definition syntax and use [] instead of array(). It is somewhat similar to the definition of arrays in JavaScript.

Use of each()

<?php
  //通过为数组元素赋值来创建数组
  $ages[&#39;trigkit4&#39;] = 22;
  echo $ages.&#39;<br/>&#39;;//Array
  //因为相关数组的索引不是数字，所以无法通过for循环来进行遍历操作，只能通过foreach循环或list()和each()结构

  //each的使用
  //each返回数组中当前的键/值对并将数组指针向前移动一步
  $users = array(&#39;trigkit4&#39;=>22,&#39;mike&#39;=>20,&#39;john&#39;=>30);
  //print_r(each($users));//Array ( [1] => 22 [value] => 22 [0] => trigkit4 [key] => trigkit4 )

  //相当于：$a = array([0]=>trigkit4,[1]=>22,[value]=>22,[key]=>trigkit4);
  $a = each($users);//each把原来的数组的第一个元素拿出来包装成新数组后赋值给$a
  echo $a[0];//trigkit4

  //!!表示将真实存在的数据转换成布尔值
  echo !!each($users);//1

?>

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

Usage of list() list is used to assign the values ​​​​of the array to some variables, see the following example:

<?php

  $a = [&#39;2&#39;,&#39;abc&#39;,&#39;def&#39;];
  list($var1,$var2) = $a;
  echo $var1.&#39;<br/>&#39;;//2
  echo $var2;//abc

  $a = [&#39;name&#39;=>&#39;trigkit4&#39;,&#39;age&#39;=>22,&#39;0&#39;=>&#39;boy&#39;];
  //list只认识key为数字的索引
  list($var1,$var2) = $a;

  echo $var1;//boy

?>

Note: only list is recognized The index where the key is a number

Sorting of array elementsReverse sorting: sort(), asort() and ksort() are all forward sorting, of course there is also a corresponding reverse sorting.
Implement reverse: rsort(), arsort() and krsort().

The array_unshift() function adds new elements to the head of the array, and the array_push() function adds each new element to the end of the array.
array_shift() deletes the first element at the head of the array. The opposite function is array_pop(), which deletes and returns an element at the end of the array.
array_rand() returns one or more keys in the array.

The function shuffle() randomly sorts the elements of the array.
Function array_reverse() gives a reverse sorting of the original array
Use of various APIs for arrayscount() and sizeof() count the number of array subscripts
array_count_values( ) Count the number of subscript values ​​in the array

<?php
  $numbers = array(&#39;100&#39;,&#39;2&#39;);
  sort($numbers,SORT_STRING);//按字符串排序，字符串只比较第一位大小
  print_r($numbers);//Array ( [0] => 100 [1] => 2 )

  $arr = array(&#39;trigkit4&#39;,&#39;banner&#39;,&#39;10&#39;);
  sort($arr,SORT_STRING);
  print_r($arr);//Array ( [0] => 10 [1] => banner [2] => trigkit4 )

  shuffle($arr);
  print_r($arr);//随机排序

  $array = array(&#39;a&#39;,&#39;b&#39;,&#39;c&#39;,&#39;d&#39;,&#39;0&#39;,&#39;1&#39;);
  array_reverse($array);
  print_r($array);//原数组的反向排序。 Array ( [0] => a [1] => b [2] => c [3] => d [4] => 0 [5] => 1 )


  //数组的拷贝
  $arr1 = array( &#39;10&#39; , 2);
  $arr2 = &$arr1 ;
  $arr2 [] = 4 ; // $arr2 被改变了,$arr1仍然是array(&#39;10&#39;, 3)
  print_r($arr2);//Array ( [0] => 10 [1] => 2 [2] => 4 )

  //asort的使用
  $arr3 = & $arr1 ;//现在arr1和arr3是一样的
  $arr3 [] = &#39;3&#39; ;
  asort($arr3);//对数组进行排序并保留原始关系
  print_r($arr3);// Array ( [1] => 2 [2] => 3 [0] => 10 )

  //ksort的使用
  $fruits = array(&#39;c&#39;=>&#39;banana&#39;,&#39;a&#39;=>&#39;apple&#39;,&#39;d&#39;=>&#39;orange&#39;);
  ksort($fruits);
  print_r($fruits);//Array ( [a] => apple [c] => banana [d] => orange )

  //unshift的使用
  array_unshift($array,&#39;z&#39;);//开头处添加一元素
  print_r($array);//Array ( [0] => z [1] => a [2] => b [3] => c [4] => d [5] => 0 [6] => 1 ) 

  //current(pos)的使用
  echo current($array);//z;获取当前数组中的当前单元

  //next的使用
  echo next($array);//a;将数组中的内部指针向前移动一位

  //reset的使用
  echo reset($array);//z;将数组内部指针指向第一个单元

  //prev的使用
  echo next($array);//a;
  echo prev($array);//z;倒回一位

  //sizeof的使用
  echo sizeof($array);//7；统计数组元素的个数

  //array_count_values
  $num = array(10,20,30,10,20,1,0,10);//统计数组元素出现的次数
  print_r(array_count_values($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 traverses

<?php
  $value = range(0,120,10);
  for($i=0;$i<count($value);$i++){
    print_r($value[$i].&#39; &#39;);//0 10 20 30 40 50 60 70 80 90 100 110 120 
  }
?>

Instance of arrayUsage of array_pad function

<?php
  //array_pad函数，数组数组首尾选择性追加
  $num = array(1=>10,2=>20,3=>30);
  $num = array_pad($num,4,40);
  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. Integers are padded to the right, and negative numbers are padded to the left.

Use of unset()

 <?php
  //unset()的使用
  $num = array_fill(0,5,rand(1,10));//rand(min,max)
  print_r($num);//Array ( [0] => 8 [1] => 8 [2] => 8 [3] => 8 [4] => 8 ) 
  echo &#39;<br/>&#39;;

  unset($num[3]);
  print_r($num);//Array ( [0] => 8 [1] => 8 [2] => 8 [4] => 8 ) 
?>

Use of array_fill()

<?php
  //array_fill()的使用
  $num = range(&#39;a&#39;,&#39;e&#39;);
  $arrayFilled = array_fill(1,2,$num);//array_fill(start,number,value)
  echo &#39;<pre class="brush:php;toolbar:false">&#39;;

  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 array members

<?php
  $color = array("red", "green", "blue", "yellow");
  count ($color); //得到4
  array_splice($color,1,1); //删除第二个元素
  print_r(count ($color)); //3
  echo $color[2]; //yellow
  echo $color[1]; //blue
?>

array_unique deletes 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() exchange The key and value of the array

<?PHP
  $array = array("red","blue","red","Black");
  print_r($array);
  echo "<br />";
  $array = array_flip($array);//
  print_r($array);//Array ( [red] => 2 [blue] => 1 [Black] => 3 ) 
?>

array_search() search value

<meta charset="utf-8">
<?php
  $array = array("red","blue","red","Black");
  $result=array_search("red",$array)//array_search(value,array,strict)
  if(($result === NULL)){
    echo "不存在数值red";
  }else{
    echo "存在数值 $result";//存在数值 0 
  }
?>

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