雄辩的javascript关联表解释 [英] eloquent javascript correlation tableFor explanation

问题描述

我正在迈出编程的第一步，我从雄辩中解决了这个问题，特别是对于weresquirrel问题。在这里：

I am taking my first steps in programming and i am stuck with this problem from eloquent, in particular with the weresquirrel problem. Here it goes :

function hasEvent(event, entry) {
 return entry.events.indexOf(event) != -1;
}

function tableFor(event, journal) {
  var table = [0, 0, 0, 0];
   for (var i = 0; i < journal.length; i++) {
     var entry = journal[i], index = 0;
      if (hasEvent(event, entry)) index += 1;
      if (entry.squirrel) index += 2;
      table[index] += 1;
 }
 return table;
}

console.log(tableFor("pizza", JOURNAL));
// → [76, 9, 4, 1]

我明白了第一个function hasevent，如果条目包含给定事件，则返回true。

I do understand the first function hasevent, it returns true if an entry contains a given event.

我无法掌握的是tableFor函数。我无法得到函数如何流动以及表如何获取其值。例如对于console.log（tableFor（pizza，JOURNAL））; ，我们得到[76,9,4,1]。但是为了上帝的缘故怎么样？

what i can't grasp is the tableFor function. I can't get how the function flows and HOW the table gets its values. For example for console.log(tableFor("pizza", JOURNAL)); , we get [76, 9, 4, 1]. But How for god's sake ?

期刊由本书提供，如下所示：

The journal is supplied by the book and looks like this :

var JOURNAL = [
  {"events":["pizza","exercise","weekend"],"squirrel":false},
  {"events":["bread","pudding","brushed teeth","weekend","touched 
  tree"],"squirrel":false},
  {"events":["carrot","nachos","brushed 
  teeth","cycling","weekend"],"squirrel":false},
  {"events":["brussel sprouts","ice cream","brushed 
  teeth","computer","weekend"],"squirrel":false},
  {"events":["potatoes","candy","brushed 
  teeth","exercise","weekend","dentist"],"squirrel":false},
  {"events":["brussel sprouts","pudding","brushed 
  teeth","running","weekend"],"squirrel":false},
  {"events":["pizza","brushed teeth","computer","work","touched 
  tree"],"squirrel":false},
  {"events":["bread","beer","brushed 
  teeth","cycling","work"],"squirrel":false},
  {"events":["cauliflower","brushed teeth","work"],"squirrel":false},
  {"events":["pizza","brushed teeth","cycling","work"],"squirrel":false},
  {"events":["lasagna","nachos","brushed teeth","work"],"squirrel":false},
  {"events":["brushed teeth","weekend","touched tree"],"squirrel":false},
  {"events":["lettuce","brushed 
   teeth","television","weekend"],"squirrel":false},
  {"events":["spaghetti","brushed teeth","work"],"squirrel":false},
  {"events":["brushed teeth","computer","work"],"squirrel":false},
  {"events":["lettuce","nachos","brushed teeth","work"],"squirrel":false},
  {"events":["carrot","brushed teeth","running","work"],"squirrel":false} ...etc

我所理解的是，一个事件作为参数传递，它通过Jounral中的对象数组来查看它是否存在。但计数如何发生？

What i understand is that an event is passed as a parameter and it looks through the array of objects in Jounral to see if it's present. But how does the counting take place ?

if (entry.squirrel) index += 2;

为什么这+2？为什么不指数+ = 3;或指数+ = 4;

Why is this +2 ? why not index += 3; or index += 4; ???

最后为什么table [index] + = 1; ????

and finally why table[index] += 1; ???

例如第一个循环是这样的：
console.log（tableFor（pizza，JOURNAL））;

For example the first loop goes like this, for : console.log(tableFor("pizza", JOURNAL));

//FLOW
i=0;

来自日记帐上面的第一行，披萨存在。

from the first line above in journal, pizza is present.

     if (hasEvent(event, entry)) index += 1;

因此索引递增并变为1.it继续：

so index is incremented and becomes 1.it continues to :

     if (entry.squirrel) index += 2; 

squirel是假的，所以没有任何索引。如果要找到squirel，为什么它+ 2 ???

squirel is false, so nothing happens to index.If squirel were to be found, why is it +2 ???

然后
表[index] + = 1
从这一点我无法理解。

then table[index] += 1 i can't understand from this point.

有人可以帮我分解一下吗？这对我的训练非常有帮助。

Can someone please break it down for me ? It would be very helpful for my training.

提前谢谢你。

推荐答案

表数组是满足不同条件的条目数。 table [3] 是 entry.squirrel 都是 hasEvent（事件）的条目数，条目）是真的。 table [2] 是只有 entry.squirrel 为真的计数， table [1 ] 是只有 hasEvent（事件，条目）为真的计数， table [0] 是两者都不为真的计数。

The table array is a count of entries that meet different criteria. table[3] is the count of entries where both entry.squirrel are hasEvent(event, entry) are true. table[2] is the count where just entry.squirrel is true, table[1] is the count where just hasEvent(event, entry) is true, and table[0] is the count where neither is true.

所以逻辑是 index 从<$ c开始$ C> 0 。如果 hasEvent（event，entry）为true，我们将 1 添加到其中。如果 entry.squirrel 为true，我们将 2 添加到其中。结果是，如果两者都是真的，我们最终添加 3 。如果两者都不是真的，我们不添加任何东西，所以它仍然是 0 。

So the logic is that index starts at 0. If hasEvent(event, entry) is true, we add 1 to it. If entry.squirrel is true we add 2 to it. The result is that if both are true, we end up adding 3. And if neither is true we don't add anything, so it's still 0.

然后我们添加 1 到 table [index] 增加该计数器。

Then we add 1 to table[index] to increment that counter.

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