我刚发现了 similar_text
函数,并且尝试使用它,但百分比输出总是让我感到惊讶。请看下面的例子。
我试图在 php: similar_text()
文档 中找到有关所使用算法的信息:
<?php
$p = 0;
similar_text('aaaaaaaaaa', 'aaaaa', $p);
echo $p . "<hr>";
//66.666666666667
//Since 5 out of 10 chars match, I would expect a 50% match
similar_text('aaaaaaaaaaaaaaaaaaaa', 'aaaaa', $p);
echo $p . "<hr>";
//40
//5 out of 20 > not 25% ?
similar_text('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'aaaaa', $p);
echo $p . "<hr>";
//9.5238095238095
//5 out of 100 > not 5% ?
//Example from PHP.net
//Why is turning the strings around changing the result?
similar_text('PHP IS GREAT', 'WITH MYSQL', $p);
echo $p . "<hr>"; //27.272727272727
similar_text('WITH MYSQL', 'PHP IS GREAT', $p);
echo $p . "<hr>"; //18.181818181818
?>
有人能解释一下这实际上是如何运作的吗?
更新:
感谢评论区的指导,我发现百分比实际上是使用相似字符数 * 200 / (长度1 + 长度2)来计算的。
Z_DVAL_PP(percent) = sim * 200.0 / (t1_len + t2_len);
这就解释了为什么百分比高于预期。使用一个字符串中的5个字符,总数为95,则计算得出10%,我可以使用这个结果。
similar_text('aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa', 'aaaaa', $p);
echo $p . "<hr>";
//10
//5 out of 95 = 5 * 200 / (5 + 95) = 10
但我仍然无法弄清楚为什么将字符串反过来时PHP返回不同的结果。dfsq提供的JS代码没有这样做。查看PHP源代码时,我只发现以下行中存在差异,但我不是C程序员。如果能提供一些有关差异的见解,将不胜感激。
在JS中:
for (l = 0;(p + l < firstLength) && (q + l < secondLength) && (first.charAt(p + l) === second.charAt(q + l)); l++);
在PHP中:(php_similar_str函数)
for (l = 0; (p + l < end1) && (q + l < end2) && (p[l] == q[l]); l++);
Source:
/* {{{ proto int similar_text(string str1, string str2 [, float percent])
Calculates the similarity between two strings */
PHP_FUNCTION(similar_text)
{
char *t1, *t2;
zval **percent = NULL;
int ac = ZEND_NUM_ARGS();
int sim;
int t1_len, t2_len;
if (zend_parse_parameters(ZEND_NUM_ARGS() TSRMLS_CC, "ss|Z", &t1, &t1_len, &t2, &t2_len, &percent) == FAILURE) {
return;
}
if (ac > 2) {
convert_to_double_ex(percent);
}
if (t1_len + t2_len == 0) {
if (ac > 2) {
Z_DVAL_PP(percent) = 0;
}
RETURN_LONG(0);
}
sim = php_similar_char(t1, t1_len, t2, t2_len);
if (ac > 2) {
Z_DVAL_PP(percent) = sim * 200.0 / (t1_len + t2_len);
}
RETURN_LONG(sim);
}
/* }}} */
/* {{{ php_similar_str
*/
static void php_similar_str(const char *txt1, int len1, const char *txt2, int len2, int *pos1, int *pos2, int *max)
{
char *p, *q;
char *end1 = (char *) txt1 + len1;
char *end2 = (char *) txt2 + len2;
int l;
*max = 0;
for (p = (char *) txt1; p < end1; p++) {
for (q = (char *) txt2; q < end2; q++) {
for (l = 0; (p + l < end1) && (q + l < end2) && (p[l] == q[l]); l++);
if (l > *max) {
*max = l;
*pos1 = p - txt1;
*pos2 = q - txt2;
}
}
}
}
/* }}} */
/* {{{ php_similar_char
*/
static int php_similar_char(const char *txt1, int len1, const char *txt2, int len2)
{
int sum;
int pos1, pos2, max;
php_similar_str(txt1, len1, txt2, len2, &pos1, &pos2, &max);
if ((sum = max)) {
if (pos1 && pos2) {
sum += php_similar_char(txt1, pos1,
txt2, pos2);
}
if ((pos1 + max < len1) && (pos2 + max < len2)) {
sum += php_similar_char(txt1 + pos1 + max, len1 - pos1 - max,
txt2 + pos2 + max, len2 - pos2 - max);
}
}
return sum;
}
/* }}} */
Javascript 代码来源:similar text 的 Javascript 移植版
&thanks=6
,这已经显示了“感谢您的投票信息”。你的链接应该是https://bugs.php.net/bug.php?id=62648,这样你才能真正地投票。 - Hugo Delsing