Detailed explanation of PHP multi-dimensional array custom sorting example

I encountered a problem today, it is like this - give you the source data, sort it and write it into a csv file. The original format is as follows:

60177=tfido=Ifmail FidoNet 兼容邮寄服务
 60179=fido=FidoNet 电子邮件和新闻网络
 10082=amandaidx=Amanda 备份服务
 10083=amidxtape=Amanda 备份服务
 1178=skkserv=简单假名到汉字（SKK）日文输入服务器
 1313=xtel=法国 Minitel 文本信息系统
 15=netstat=网络状态（netstat）
 1529=support [prmsd, gnatsd]=GNATS 错误跟踪系统
 2=nbp=名称绑定协议
 2003=cfinger=GNU Finger 服务
 22289=wnn4_Cn=cWnn 中文输入系统
 22305=wnn4_Kr=kWnn 韩文输入系统
 22321=wnn4_Tw=tWnn 中文输入系统（台湾）
 2430=venus=用于 Coda 文件系统（codacon 端口）的 Venus 缓存管理器
 2430=venus=用于 Coda 文件系统（callback/wbc interface 界面）的 Venus 缓存管理器
 2431=venus-se=Venus 传输控制协议（TCP）的副作用
 2431=venus-se=Venus 用户数据报协议（UDP）的副作用
 2432=codasrv=Coda 文件系统服务器端口
 2433=codasrv-se=Coda 文件系统 TCP 副作用
 2433=codasrv-se=Coda 文件系统 UDP SFTP 副作用
 3128=squid=Squid 万维网代理缓存
 4=echo=AppleTalk Echo 协议
 4557=fax=FAX 传输服务（旧服务）
 4559=hylafax=HylaFAX 客户-服务器协议（新服务）
 465=smtps=通过安全套接字层的简单邮件传输协议（SMTPS）

My method is to read in the file function, and thenforeachLoop to get a two-dimensional array:

<?PHP
 
     $file = file(&#39;4.txt&#39;);
     $data = array();
     foreach($file as $key=>$value){
         $data[] = explode(&#39;=&#39;,$value);
 
     }
?>

The format of this two-dimensional array becomes like this:

<?php
array(
    [0]=>array([0]=>23,[1]=>Telnet,[2]=>&#39;远程。。&#39;)
    [1]=>array([0]=>2,[1]=>Telnet,[2]=>&#39;远程。。&#39;)
)
?>

Think about using PHP functions After sorting, I suddenly discovered that this is a two-dimensional array. Most of PHP's own sorting is for one dimension. This is why I have to use the Usort function to customize the sorting. The code is as follows

<?PHP
 
     $file = file(&#39;4.txt&#39;);
     $data = array();
     foreach($file as $key=>$value){
         $data[] = explode(&#39;=&#39;,$value);
 
     }
     function arrSort($a,$b){
         if(!is_array($a)||!is_array($b)){
             echo $a,$b;
             die(&#39;出现非数组&#39;);
         }
         return ($a[0]>$b[0])?1:-1;
     }
     usort($data,&#39;arrSort&#39;);
     
 
 ?>

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