将d3.max与数组数组嵌套

问题描述

我有一个像这样的数组数组。

I have an array of arrays like so.

data = [
  [
    {x: 1, y: 40},
    {x: 2, y: 43},
    {x: 3, y: 12},
    {x: 4, y: 60},
    {x: 5, y: 63},
    {x: 6, y: 23}
 ], [
    {x: 1, y: 12},
    {x: 2, y: 5},
    {x: 3, y: 23},
    {x: 4, y: 18},
    {x: 5, y: 73},
    {x: 6, y: 27}
 ], [
    {x: 1, y: 60},
    {x: 2, y: 49},
    {x: 3, y: 16},
    {x: 4, y: 20},
    {x: 5, y: 92},
    {x: 6, y: 20}
  ] 
];

我可以找到带有嵌套d3的 data 的最大y值。 max（）调用：

I can find the maximum y value of data with a nested d3.max() call:

d3.max(data, function(d) {
  return d3.max(d, function(d) {
    return d.y;
  });
});

我正在努力了解此代码的实际工作方式。我知道d3.max（）函数的第二个参数指定了一个访问器函数-但我对调用d3.max（）两次与访问器函数的确切关联感到困惑。

I'm struggling to understand how this code actually works. I know the second argument of the d3.max() function specifies an accessor function - but I'm confused into how exactly calling d3.max() twice relates with the accessor function.

我想我要问的是有关JavaScript如何解释此代码的演练。我已经在控制台上浏览了它，但不幸的是它没有帮助。

I guess what I'm asking for is a walkthrough of how javascript interprets this code. I've walked through it on the console but it didn't help unfortunately.

推荐答案

有时，这全都与变量的命名有关：

Sometimes it's all about the naming of the variables:

// the outer function iterates over the outer array
// which we can think of as an array of rows

d3.max(data, function(row) {

  // while the inner function iterates over the inner
  // array, which we can think of as an array containing
  // the columns of a single row. Sometimes also called
  // a (table) cell.

  return d3.max(row, function(column) {
    return column.y;
  });

});

您可以在此处找到d3.max函数的源代码：

You can find the source code for the d3.max function here: https://github.com/d3/d3.github.com/blob/8f6ca19c42251ec27031376ba9168f23b9546de4/d3.v3.js#L69

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