PHP string learning counts the number of occurrences of characters

In the previous article, we introduced a case-insensitive method of replacing a given substring with other values. If you are interested, you can click on the link to check → "PHP cleverly uses functions to replace a given substring with * Number (case insensitive) 》. This time we will introduce how to use PHP to count the number of occurrences of characters in a string. You can refer to it if necessary.

I believe that given a string "aaabbccqqwweeab", how to count the number of occurrences of each character? You can use the loop

<?php
header("Content-Type: text/html;charset=utf-8");    //设置字符编码
//统计字符串中出现的字符，出现次数
$str = &#39;aaabbccqqwweeab&#39;;//字符串示例
echo "字符串为：".$str.&#39;<br/>&#39;;
$strRecord=array();//把出现过的字符记录在此数组中，如果记录有，则不记录，
for($i=0;$i<strlen($str);$i++){
 $found = 0;//默认设置为没有遇到过
 foreach((array)$strRecord as $k=>$v){
  if($str[$i] == $v[&#39;key&#39;]){
   $strRecord[$k][&#39;count&#39;] += 1;//已经遇到，count + 1；
   $found = 1;//设置已经遇到过的，标记
   continue;//如果已经遇到，不用再循环记录数组了，继续下一个字符串比较
  }
 }
 if(!$found){
  $strRecord[] = array(&#39;key&#39;=>$str[$i],&#39;count&#39;=>1);//记录没有遇到过的字符串
 }
}
echo &#39;<pre class="brush:php;toolbar:false">&#39;;
print_r($strRecord);
?>

to analyze:

• Loop the $str string once and record the characters that have appeared in the $strRecord array (only record once, if repeated, Just ignore it).

• Traverse the $strRecord array and compare each character in the string ($str[$i]) with the value of the array ($strRecord[ ]['key']) for comparison; if a value in the record is the same as this character, record the number of times ($strRecord[]['count']) 1.

Let’s take a look at the output:

OK, the statistics are out!

But sometimes we don’t need to count all characters, we only need to count the number of occurrences of a specified character/substring. How to do this?

This is also simple, PHP provides a built-in function to solve this problem. Let's take a look at the following example:

<?php
header("Content-Type: text/html;charset=utf-8");    //设置字符编码
$str = &#39;aaabbccqqwweeab&#39;;
echo "字符串为：".$str.&#39;<br/><br/>&#39;;

echo "字符串中出现了 ".substr_count($str,&#39;a&#39;)." 次 a字符!";

echo "<br/><br/>字符串中出现了 ".substr_count($str,&#39;ab&#39;)." 次 ab子串!";
?>

Analysis: We use "substr_count($str,'a')" and "substr_count($str,'ab') " statement to count the number of occurrences of the "a" character and the "ab" character in the string $str. What do you think this will output? Should "4" and "2" be output? So right? Let's take a look at the output:

Correct! The number of occurrences of the "a" character and the "ab" character is "4" and "2".

Let’s take a look at the key function substr_count().

The substr_count() function can count the number of times a substring (consisting of one or more characters) appears in a string (case-sensitive).

substr_count($string,$substring,$start,$length)The function accepts 2 required parameters $string and $substring, and 2 omitted parameters $start and $length.

We already know the first two required parameters through the above code example. Let's take a look at the two omitted parameters $start and $length.

• $start: used to specify where to start searching for substrings in the string

• $length: used to specify the length of the search

The value returned by the substr_count() function is also different depending on the values ​​set by the parameters $start and $length.

<?php
header("Content-Type: text/html;charset=utf-8");    //设置字符编码
$str = &#39;aaabbccqqwweeab&#39;;
echo "字符串为：".$str.&#39;<br/><br/>&#39;;

echo "字符串中出现了 ".substr_count($str,&#39;a&#39;,0,5)." 次 a字符!";
echo "<br/>字符串中出现了 ".substr_count($str,&#39;a&#39;,2,5)." 次 a字符!";
echo "<br/><br/>字符串中出现了 ".substr_count($str,&#39;ab&#39;,0,10)." 次 ab子串!";
echo "<br/>字符串中出现了 ".substr_count($str,&#39;ab&#39;,3)." 次 ab子串!";
?>

Output result:

Okay, that’s all. If you want to know anything else, you can click this. → →php video tutorial

Finally, I recommend reading a classic course "PHP String Processing (Jade Girl Heart Sutra Edition)", it's free~ come and learn !

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