[英]Explain how the phi coefficient function works in Eloquent Javascript?
I'm currently reading Eloquent Javascript and so far it's been a good read, but I'm stuck on this one function that he's put up, for calculating the phi-coeffcient. 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功能,用于计算phi-coeffcient。 This is the code.
这是代码。
There's obviously quite a bit of context for it, and I can't copy/paste everything off the book, so if someone who's actually read the book could explain this to me, it would be awesome! 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!
What I don't get is, what is being referred to when he says "table[3]", or "table[0]"? 我没有得到的是,当他说“table [3]”或“table [0]”时会提到什么? I understand the phi coefficient formula:
我理解phi系数公式:
ϕ = (n11n00 - n10n01) / (√ n1•n0•n•1n•0) φ=(n11n00 - n10n01)/(√n1•n0•n•1n•0)
But I don't get (at all) how he's translated that into JS. 但是我(根本没有)如何将它翻译成JS。 What exactly is happening in this code?
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]));
}
Try to visualize the process on each step, and substitute, like an equation: 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]))
}
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