我在“单线”之后写了一个用于归一化向量的向量（这里用通常的数组表示），这意味着将每个条目除以向量的欧几里得范数。
<table id="table-1" class="table table-hover">
<thead>
<tr>
<th>test</th>
<th>test</th>
<th>test</th>
<th>test</th>
<th>test</th>
<th>test</th>
<th>test</th>
<th>test</th>
<th>test</th>
<th>test</th>
<th>test</th>
<th>test</th>
<th>test</th>
</tr>
</thead>
<body>
<div class="content">
<table class="table table-striped">
<tbody>
<tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr>
<tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr>
<tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr>
<tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr>
<tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr>
<tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr><tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr>
<tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr>
<tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr>
<tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr>
<tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr>
<tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr>
<tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr><tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr>
<tr class="bordered">
<td align="center">test </td>
<td align="center">test </td>
<td align="center"> test</td>
<td align="center"> test </td>
<td align="center" data-toggle="modal"
id="myBtn">
test </td>
<td align="center"> test</td>
<td align="center">
test</td>
<td align="center"> test </td>
<td align="center"> test </td>
<td align="center"> test </td>
<td>
test
</td>
<td>
test
</td>
<td>
test
</td>
</tr>
</tbody>
</table>
<table id="header-fixed"></table>
var tableOffset = $("#table-1").offset().top;
var $header = $("#table-1 > thead").clone();
var $fixedHeader = $("#header-fixed").append($header);
$(window).bind("scroll", function() {
var offset = $(this).scrollTop();
if (offset >= tableOffset && $fixedHeader.is(":hidden")) {
$fixedHeader.show();
}
else if (offset < tableOffset) {
$fixedHeader.hide();
}
});
不幸的是，它不是非常有效，因为该规范是针对每个条目一遍又一遍地计算的。我们能否以避免重复评估的方式修改此“单线”？
编辑：我发现的一种方法-并不是特别优雅且不易读-需要在最外层的lambda上添加另一个输入参数，并将其用作规范的输入：
normalize = v => v.map(x => x/Math.sqrt(v.map(x => x * x).reduce((a, b) => a + b)))
答案 0 :(得分：0)
只是不要尝试变得太聪明...
const normalize = v => {
const norm = Math.sqrt(v.map(x => x * x).reduce((a, b) => a + b)));
return v.map(x => x / norm);
};