Notes on commonly used array operation methods in PHP, array operation methods_PHP tutorial

Collection of notes on commonly used array operation methods in PHP, overview of array operation methods

To access the contents of a variable, 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 on arrays
PHP defines array:

<&#63;php 
  $array = array(); 
  $array["key"] = "values"; 
&#63;> 

There are two main ways to declare arrays in PHP:

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

<&#63;php
  //array数组
  $users = array('phone','computer','dos','linux');
  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 '<br/>';
  }

//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 '<br/>';
  }
//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.'<br/>';//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.'<br/>';//输出键
  }
&#63;>

Create an array of custom keys

<&#63;php

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

  echo $ceo['apple'];//jobs

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

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

&#63;>  

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

Usage of each()

<&#63;php
  //通过为数组元素赋值来创建数组
  $ages['trigkit4'] = 22;
  echo $ages.'<br/>';//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
  $users = array('trigkit4'=>22,'mike'=>20,'john'=>30);
  //print_r(each($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

&#63;> 

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

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

<&#63;php

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

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

  echo $var1;//boy

&#63;>

Note: list only recognizes indexes whose keys are numbers

Sort of array elements
Reverse sorting: sort(), asort() and ksort() are all forward sorting, and of course there is 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 an array.

The function shuffle() randomly sorts the elements of the array.
The function array_reverse() gives a reverse sort of the original array
Uses of various APIs for arrays
count() and sizeof() count the number of array subscripts
array_count_values() counts the number of subscript values ​​in the array

<&#63;php
  $numbers = array('100','2');
  sort($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 )

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

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

  $array = array('a','b','c','d','0','1');
  array_reverse($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( '10' , 2);
  $arr2 = &$arr1 ;
  $arr2 [] = 4 ; // $arr2 被改变了,$arr1仍然是array('10', 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
  $arr3 [] = '3' ;
  asort($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
  $fruits = array('c'=>'banana','a'=>'apple','d'=>'orange');
  ksort($fruits);
  print_r($fruits);//Array ( [a] => apple [c] => banana [d] => orange )

  //unshift的使用
  array_unshift($array,'z');//开头处添加一元素
  print_r($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 ) 

&#63;>  

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

<&#63;php
  $value = range(0,120,10);
  for($i=0;$i<count($value);$i++){
    print_r($value[$i].' ');//0 10 20 30 40 50 60 70 80 90 100 110 120 
  }
&#63;>

Instance of array
Usage of array_pad function

<&#63;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 ) 
&#63;>

size: specified length. Integers are padded to the right, and negative numbers are padded to the left.

Usage of unset()

 <&#63;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 '<br/>';

  unset($num[3]);
  print_r($num);//Array ( [0] => 8 [1] => 8 [2] => 8 [4] => 8 ) 
&#63;>

Usage of array_fill()

<&#63;php
  //array_fill()的使用
  $num = range('a','e');
  $arrayFilled = array_fill(1,2,$num);//array_fill(start,number,value)
  echo '<pre class="brush:php;toolbar:false">';

  print_r($arrayFilled);

&#63;>

Usage of array_combine()

<&#63;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 ) 
&#63;> 

array_splice() deletes array members

<&#63;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
&#63;> 

array_unique removes duplicate values ​​in an array

<&#63;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 ) 
&#63;> 

array_flip() exchanges the key and value of the array

<&#63;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 ) 
&#63;> 

array_search() search value

<meta charset="utf-8">
<&#63;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 
  }
&#63;> 

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