eloquent javascript相关表解释 [英] eloquent javascript correlation tableFor explanation

问题描述

我正在迈出编程的第一步，但我从 eloquent 开始就被这个问题困住了，尤其是在 wassquirrel 问题上.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]

我确实理解第一个函数 hasevent，如果条目包含给定事件，它返回 true.

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

我无法理解的是 tableFor 函数.我不知道函数是如何流动的，以及表是如何获得它的值的.例如对于 console.log(tableFor("pizza", JOURNAL));，我们得到 [76, 9, 4, 1].但是看在上帝的份上怎么办?

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 ?

期刊由书提供，看起来像这样:

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

我的理解是，事件作为参数传递，它会查看日志中的对象数组以查看它是否存在.但是计数是如何进行的呢?

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;

为什么是 +2 ?为什么不索引 += 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，对于:console.log(tableFor("pizza", JOURNAL));

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

//FLOW
i=0;

从日志上面的第一行开始，披萨是存在的.

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

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

所以索引增加并变成1.它继续:

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

     if (entry.squirrel) index += 2; 

squirel 是假的，所以索引没有任何变化.如果找到了松鼠，为什么它是 +2 ???

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

然后表[索引] += 1从这一点上我无法理解.

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

谁能帮我分解一下?这对我的训练很有帮助.

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

先谢谢你.

推荐答案

table 数组是满足不同条件的条目的计数.table[3] 是 entry.squirrel 和 hasEvent(event, entry) 都为真的条目数.table[2] 是 entry.squirrel 为真的计数，table[1] 是 hasEvent(event, entry) 为真，并且 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 0 开始.如果 hasEvent(event, entry) 为真，我们添加 1 到它.如果 entry.squirrel 为真，我们添加 2 到它.结果是，如果两者都为真，我们最终添加了 3.如果两者都不是，我们就不添加任何东西，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.

然后我们将 1 添加到 table[index] 以增加该计数器.

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

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