请帮助我理解select（）和selectAll（）之间的区别， [英] Please help me understand the difference between the select() and selectAll()

问题描述

我觉得我误解了一些非常基本的，这两者之间的区别是什么？

I feel I misunderstand something very basic, what is the difference between those two ?

我没有得到第二个不追加ap标签的原因对我来说。

I didn't get the reason why the second one will not append a p tag for me.

divSelection = d3.select('#div-vis').selectAll('p').data(['dummy']).enter().append('p');

divSelection = d3.select('#div-vis').select('p').data(['dummy']).enter().append('p');

推荐答案

从嵌套选择：

嵌套选择有另一个微妙但关键副作用：它为每个组设置父节点。父节点是选择项上的隐藏属性，用于确定在哪里附加输入元素。 ... select和selectAll之间有一个重要的区别：select保留现有分组，而selectAll创建一个新分组。因此调用select会保留数据，索引，甚至是原始选择的父节点！

Nesting selections has another subtle yet critical side-effect: it sets the parent node for each group. The parent node is a hidden property on selections that determines where to append entering elements. … There is an important difference between select and selectAll: select preserves the existing grouping, whereas selectAll creates a new grouping. Calling select thus preserves the data, index and even the parent node of the original selection!

当你说 d3.select（＃vis），选择的父节点仍然是文档元素。然后，当您说 selectAll（p）时，您将父节点定义为先前选择的#vis元素，因为selectAll是嵌套运算符。这只发生在selectAll而不是选择。

When you say d3.select("#vis"), the parent node of the selection is still the document element. When you then say selectAll("p"), you define the parent node as the previously-selected #vis element, because selectAll is a nesting operator. That only happens with selectAll and not select.

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