为什么这个D3代码添加了 <p> 身体外的元素，而不是它内部？

Question

I'm learning D3 and have come across an issue using the select operator. 我正在学习D3并且使用select运算符遇到了一个问题。

Specifically, why does the following code add the <p> element outside the body, instead of inside it? 具体来说，为什么以下代码将<p>元素添加到正文之外，而不是在其中？

var pData1 = d3.select("body").select("p").data([1]).enter().append("p");

I am using a totally blank HTML file with just <head> and <body> tags to test. 我正在使用一个完全空白的HTML文件，只需<head>和<body>标签进行测试。

<html lang="en">
<head>
<title><!-- Insert your title here --></title>
  <script type="text/javascript" src="d3.min.js"></script>
</head>
<body>

</body>
</html>

Answer 1

(This repeats the content from Lars Kotthoff's answer, but I'd spent time creating the demo so I thought I'd still post.) （这重复了Lars Kotthoff的回答中的内容，但我花时间创建了演示，所以我想我还会发帖。）

The problem is that select , unlike selectAll , does not re-define the parent element for elements added in the enter() selection. 问题是，与selectAll不同， select不会为enter()选择中添加的元素重新定义父元素。

d3.select("body").select("p#a")
    .data([1])
    .enter().append("p").attr("id", "a")
    .text("This paragraph is appended to <html> (the document root) 
          because no selectAll statement reset the parent element.");

d3.selectAll("p#b")
    .data([1])
    .enter().append("p").attr("id", "b")
    .text("This paragraph is appended to <html> 
          because the selectAll statement is called directly on the root.");

d3.selectAll("body").select("p#c")
    .data([1])
    .enter().append("p").attr("id", "c")
    .text("This paragraph is also appended to <html> 
          because the last selectAll statement was called directly from the root.");

d3.select("body").selectAll("p#d")
    .data([1])
    .enter().append("p").attr("id", "d")
    .text("This paragraph is appended to <body> 
          because the selectAll statement is a sub-selection of the body selection.");

d3.selectAll("body").selectAll("p#e")
    .data([1])
    .enter().append("p").attr("id", "e")
    .text("This paragraph is also appended to <body> 
          because the final selectAll statement is a sub-selection of the body.");

http://fiddle.jshell.net/eLF4H/ http://fiddle.jshell.net/eLF4H/

It is unusual to use an enter chain after a select statement (versus selectAll), because usually you are selecting multiple elements if you are going to do a data join. 在select语句之后使用输入链是不常见的（与selectAll相比），因为如果要进行数据连接，通常会选择多个元素。 However, if you want to create the element if it doesn't exist or update it if it does , you have two options: 但是， 如果要创建元素（如果它不存在）或者更新它，则有两个选项：

use a selectAll statement followed by the data join 使用selectAll语句后跟数据连接

 var pdata1 = d3.select("body").selectAll("p#data") //select element if it exists .data([dataObject]); //join to the current data pdata1.enter().append("p").attr("id", "data"); //create element if required pdata1.text(function(d){return d.textValue;}); //set or update the element based on the data

use an if statement to create the element if necessary and use .datum() to bind the data 如果需要，使用if语句创建元素，并使用.datum()绑定数据

 var pdata1 = d3.select("p#data") //select element if it exists if ( pdata1.empty() ) { pdata1 = d3.select("body").append("p").attr("id", "data"); //create element if required } pdata1.datum(dataObject) //note that you don't need to put the data into an array .text(function(d){return d.textValue;}); //set or update the element based on the data

Answer 2

As suggested in the comments, the way to do what you're trying to do is to use .selectAll() . 正如评论中所建议的那样，你要做的就是使用.selectAll() 。 The difference between .select() and .selectAll() is that .select() returns elements while .selectAll() returns elements grouped by ancestor . 之间的差.select()和.selectAll()是.select()返回元件，同时.selectAll()返回由祖先分组元素 。 This then affects any subsequent .data() operations in terms of what the elements are appended to. 然后，这将根据元素的附加内容影响任何后续的.data()操作。 From the documentation : 从文档：

Grouping by selectAll also affects subsequent entering placeholder nodes. selectAll分组也会影响后续进入的占位符节点。 Thus, to specify the parent node when appending entering nodes, use select followed by selectAll: 因此，要在添加进入节点时指定父节点，请使用select后跟selectAll：

d3.select("body").selectAll("div") d3.select（ “身体”）。全选（ “分区”）

Answer 3

there is no p element to select, so I would suggest appending the p element before entering your data: 没有p元素可供选择，所以我建议在输入数据之前附加p元素：

var pData1 = d3.select("body").append("p")

pData1.data([1])...

do whatever else you need to do after .data, although there is no need to append another p 做任何你需要做的事情.data，虽然没有必要追加另一个p

为什么这个D3代码添加了 <p> 身体外的元素，而不是它内部？

问题描述

3 个解决方案

解决方案1
13 已采纳 2014-05-04 19:07:53

解决方案2
3 2014-05-04 18:42:41

解决方案3
2 2014-05-04 18:33:52

为什么这个D3代码添加了 <p> 身体外的元素，而不是它内部？

问题描述

3 个解决方案

解决方案1 13 已采纳 2014-05-04 19:07:53

解决方案2 3 2014-05-04 18:42:41

解决方案3 2 2014-05-04 18:33:52

解决方案1
13 已采纳 2014-05-04 19:07:53

解决方案2
3 2014-05-04 18:42:41

解决方案3
2 2014-05-04 18:33:52