this post was submitted on 25 Nov 2023
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Machine Learning

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hi everyone, I could not understand answer. I found 1/4 from table. answer is 1/2. thanks everyone.

https://preview.redd.it/tht330mp7h2c1.png?width=939&format=png&auto=webp&s=2084932c8e79929563ddc757f012fce0c040453c

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[–] mofoss@alien.top 1 points 11 months ago (2 children)

P(K=1) = 1/2

P(a=1|K=1) = P(a=1,K=1)/P(K=1) = (1/4)/(1/2)=1/2

P(b=1|K=1) = P(b=1,K=1)/P(K=1) = (1/8)/(1/2)=1/4

P(c=0|K=1) = P(c=0, K=1)/P(K=1) = (1/4)/(1/2)=1/2

P(a=1, b=1, c=0, K=1) = 0

P(a=1, b=1, c=0, K=0) = 1/8

[0.5 * 0.25 * 0.5] / (0 + 1/8) = (1/16) / (1/8) = 1/2

For conditionals, convert it into joints and priors first and THEN use the table to count instances out of N samples.

P(X|Y) = P(X,Y)/P(Y)

:)

[–] Terrible_Button_1763@alien.top 1 points 11 months ago (2 children)

At the very least your calculation does not agree with your formula of P(X|Y) = P(X,Y)/P(Y).

How is the numerator a calculation of P(X,Y)? [0.5 * 0.25 * 0.5] is P(a = 1 | K =1 ) * P(b = 1 | K = 1) * P(c = 0 | K = 1) which is (in Naive Bayes) P(X|Y) by Naive Bayes and not P(X, Y).

[–] mofoss@alien.top 1 points 11 months ago (1 children)

Uh not sure what Fubini's theorem is, I just use the equivalence of P(X|Y)P(Y) = P(Y|X)P(X) = P(X,Y)

[–] Terrible_Button_1763@alien.top 1 points 11 months ago (1 children)

That's not what the questions is asking. And that's not Bayes' rule. The denominator is not even calculating P(Y) under Naive Bayes.

Hmm, maybe machine learning is not just import tensorflow/pytorch/llm.

[–] mofoss@alien.top 1 points 11 months ago (1 children)

Features are independent when conditioned on the dependent is pretty much what I know about Naive Bayes, I personally don't care for the semantics.

Also the last time I was using naive bayes was grad school 7 years ago so things are fuzzy, sorry

[–] Terrible_Button_1763@alien.top 1 points 11 months ago

Save it for your next submission, friend.

[–] mofoss@alien.top 1 points 11 months ago (1 children)

Oh wait I made a typo, OP ignore my answer 😅

[–] mofoss@alien.top 1 points 11 months ago
[–] Kruki37@alien.top 1 points 11 months ago (1 children)

Seems like you dropped one of the 1/2s from the numerator. Maybe I’m missing something but the answer looks like 1/4 to me as your workings show

[–] Terrible_Button_1763@alien.top 1 points 11 months ago

I rate your answer 🌶️🌶️🌶️🌶️🌶️ / this dumpster fire.