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Fix median for Binomial distribution #1924

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Merged
devmotion merged 7 commits into from
Dec 14, 2024
Merged

Fix median for Binomial distribution #1924

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ff5cf46
Fix `median` for `Binomial`
marcusps Dec 13, 2024
515c5e2
Merge pull request #1 from marcusps/marcusps/fix-binomial-median
marcusps Dec 13, 2024
0f2fed8
Add tests for `median(x::Binomial)`
marcusps Dec 14, 2024
f0275a3
Remove specialization of `median` to `Binomial`
marcusps Dec 14, 2024
e9aa32e
Merge pull request #2 from marcusps/marcusps/fix-binomial-median
marcusps Dec 14, 2024
9bb0947
Update R reference
devmotion Dec 14, 2024
b3c557b
Simplify test
devmotion Dec 14, 2024
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2 changes: 0 additions & 2 deletions src/univariate/discrete/binomial.jl
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Expand Up @@ -73,8 +73,6 @@ function mode(d::Binomial{T}) where T<:Real
end
modes(d::Binomial) = Int[mode(d)]

median(d::Binomial) = round(Int,mean(d))

function skewness(d::Binomial)
n, p1 = params(d)
p0 = 1 - p1
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2 changes: 1 addition & 1 deletion test/ref/discrete/binomial.R
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Expand Up @@ -18,7 +18,7 @@ Binomial <- R6Class("Binomial",
failprob=q,
ntrials=n,
mean=n * p,
median=round(n * p),
median=qbinom(0.5, self$n, self$p),
var=n * p * q,
skewness=(q - p) / sqrt(n*p*q),
kurtosis=(1 - 6*p*q) / (n*p*q))
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2 changes: 1 addition & 1 deletion test/ref/discrete_test.ref.json
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Expand Up @@ -285,7 +285,7 @@
"failprob": 0.5,
"ntrials": 3,
"mean": 1.5,
"median": 2,
"median": 1,
"var": 0.75,
"skewness": 0,
"kurtosis": -0.666666666666667
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7 changes: 7 additions & 0 deletions test/univariate/discrete/binomial.jl
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Expand Up @@ -26,6 +26,13 @@ end
@test Distributions.expectation(identity, Binomial(6)) ≈ 3.0
@test Distributions.expectation(x -> -x, Binomial(10, 0.2)) ≈ -2.0

# Test median
@test median(Binomial(5,3//10)) == 1
@test median(Binomial(25,3//10)) == 7
@test median(Binomial(45,3//10)) == 13
@test median(Binomial(65,3//10)) == 19
@test median(Binomial(85,3//10)) == 25

# Test mode
@test Distributions.mode(Binomial(100, 0.4)) == 40
@test Distributions.mode(Binomial(1, 0.51)) == 1
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