解释phi系数函数如何在Eloquent Javascript中工作？

Question

我目前正在阅读Eloquent Javascript,到目前为止,这是一个很好的阅读,但我仍然坚持他提出的这个函数,用于计算phi-coeffcient.这是代码.

显然有相当多的背景,我无法复制/粘贴书中的所有内容,所以如果真正读过这本书的人可以向我解释这一点,那就太棒了!

我没有得到的是,当他说"table [3]"或"table [0]"时会提到什么？我理解phi系数公式:

φ=(n11n00 - n10n01)/(√n1•n0•n•1n•0)

但是我(根本没有)如何将它翻译成JS.这段代码究竟发生了什么？

function phi(table) {
  return (table[3] * table[0] - table[2] * table[1]) /
    Math.sqrt((table[2] + table[3]) *
              (table[0] + table[1]) *
              (table[1] + table[3]) *
              (table[0] + table[2]));
}

Answer 1

尝试将每个步骤的过程可视化,并替换为等式:

???????????????????????????????
? label: n00   ? label: n01   ?
? count: 76    ? count: 9     ?
? no squirrel, ? no squirrel, ?
? no pizza     ? pizza        ?
???????????????????????????????
? label: n10   ? label: n11   ?
? count: 4     ? count: 1     ?
? squirrel,    ? squirrel,    ?
? no pizza     ? pizza        ?
???????????????????????????????

table = [n00, n01, n10, n11]

n00 = table[0] = 76
n10 = table[1] = 4
n01 = table[2] = 9
n11 = table[3] = 1

n1• = n10 + n11 = table[2] + table[3] = 9  + 1 = 10
n0• = n00 + n01 = table[0] + table[1] = 76 + 4 = 80
n•1 = n01 + n11 = table[1] + table[3] = 4  + 1 = 5
n•0 = n00 + n10 = table[0] + table[2] = 76 + 9 = 85

//pseudo code
phi = function(table) {
  return (n11 * n00 - n10 * n01) /
    Math.sqrt(n1• * n0• * n•1 * n•0)
}

//JavaScript code
phi = function(table) {
  return (table[3] * table[0] - table[2] * table[1]) /
    Math.sqrt((table[2] + table[3]) *
              (table[0] + table[1]) *
              (table[1] + table[3]) *
              (table[0] + table[2]))
}