javascript jQuery：如何计算所有匹配元素的最大属性值？
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jQuery: How to calculate the maximal attribute value of all matched elements?
提问by Misha Moroshko
Consider the following HTML:
考虑以下 HTML：
<div class="a" x="6"></div>
<div class="a" x="9"></div>
<div class="a" x="2"></div>
...
<div class="a" x="8"></div>
How would you find the maximal xvalue of all .aelements ?
你将如何找到x所有.a元素的最大值？
Assume that all xvalues are positive integers.
假设所有x值都是正整数。
回答by Blender
Just loop over them:
只需循环它们：
var maximum = null;
$('.a').each(function() {
var value = parseFloat($(this).attr('x'));
maximum = (value > maximum) ? value : maximum;
});
回答by topek
I got another version:
我得到了另一个版本：
var numbers = $(".a").map(function(){
return parseFloat(this.getAttribute('x')) || -Infinity;
}).toArray();
$("#max").html(Math.max.apply(Math, numbers));
This uses the map function to extract the values of the x-Attributes, converts the object into an array and provides the array elements as function parameters to Math.max
这使用 map 函数来提取 x-Attributes 的值，将对象转换为数组并将数组元素作为函数参数提供给 Math.max
The Math.max trick was stolen from http://ejohn.org/blog/fast-javascript-maxmin/
Math.max 技巧是从http://ejohn.org/blog/fast-javascript-maxmin/窃取的
UPDATE
更新
add "|| -Infinity" to process the case correctly, when no attribute is present. See fiddle of @kubedan
添加“|| -Infinity”以在不存在属性时正确处理案例。见@kubedan的小提琴
回答by Ben Taliadoros
回答by Erick Petrucelli
I was doing some tests regarding this topic, and if performance matters, a old but gold simple forwould be better than jQuery.map(), Math.apply()and also Array.sort():
我正在做一些关于这个主题的测试，如果性能很重要，一个旧但金色的简单for会比jQuery.map()，Math.apply()而且Array.sort()：
var items = $(".a");
for (var i = 0; i < items.length; i++) {
var val = items.eq(i).prop('x');
if (val > max) max = val;
}
Here are the jsperftests: http://jsperf.com/max-value-by-data-attribute. Nothing really drastic, but interesting anyway.
以下是jsperf测试：http: //jsperf.com/max-value-by-data-attribute。没有什么特别激烈的，但无论如何都很有趣。
回答by nnnnnn
var max = null;
$('.a').each(function() {
var x = +($(this).attr('x'));
if (max === null || x > max)
max = x;
}
alert(max === null ? "No matching elements found" : "The maximum is " + max);
Note the unary +operator to convert the attribute to a number. You may want to add some error checking to ensure it actually isa number - and that the attribute exists at all. You could change the selector to only select elements with the class and the attribute: $('.a[x]').
请注意+将属性转换为数字的一元运算符。您可能想要添加一些错误检查以确保它实际上是一个数字 - 并且该属性根本存在。您可以将选择器更改为仅选择具有类和属性的元素：$('.a[x]')。
回答by Kanishka Panamaldeniya
var max =0;
$('.a').each(function(){
if(parseFloat($(this).attr('x'))>max)
{
max = parseFloat($(this).attr('x')) ;
}
});
alert(max);
