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Fix mode(Binomial) and modes(Binomial) #1931

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Fix mode(Binomial) and modes(Binomial) #1931

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194adf9
Returns smallest `mode` in `mode(Binomial)`, fix `modes`
marcusps Dec 17, 2024
ea39724
Update tests for mode(Binomial) and modes(Binomial)
marcusps Dec 17, 2024
87df67f
Fix incorrect test
marcusps Dec 19, 2024
1116bf1
Add a few more tests
marcusps Dec 19, 2024
0fac6c0
Fix bug with mode calculation condition
marcusps Dec 19, 2024
6c0abd5
Merge branch 'master' into marcusps/fix-mode
marcusps Dec 19, 2024
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31 changes: 28 additions & 3 deletions src/univariate/discrete/binomial.jl
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Original file line number Diff line number Diff line change
Expand Up @@ -67,11 +67,36 @@ params(d::Binomial) = (d.n, d.p)

mean(d::Binomial) = ntrials(d) * succprob(d)
var(d::Binomial) = ntrials(d) * succprob(d) * failprob(d)
function mode(d::Binomial{T}) where T<:Real

function mode(d::Binomial)
(n, p) = params(d)
v = (n + 1) * p
quasi_mode = floor(Int, v)
if quasi_mode == v && p > 0
if p == 1
n
else
quasi_mode-1
end
else
quasi_mode
end
end

function modes(d::Binomial)
(n, p) = params(d)
n > 0 ? floor(Int, (n + 1) * d.p) : zero(T)
v = (n + 1) * p
quasi_mode = floor(Int, v)
if quasi_mode == v
if p == 1
Int[n]
else
Int[quasi_mode-1, quasi_mode]
end
else
Int[quasi_mode]
end
end
modes(d::Binomial) = Int[mode(d)]

function median(dist::Binomial)
# The median is floor(Int, mean) or ceil(Int, mean)
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17 changes: 14 additions & 3 deletions test/univariate/discrete/binomial.jl
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Expand Up @@ -35,9 +35,20 @@ end
@test all(median(Binomial(7, p)) == quantile(Binomial(7, p), 1//2) for p in 0:0.1:1)

# Test mode
@test Distributions.mode(Binomial(100, 0.4)) == 40
@test Distributions.mode(Binomial(1, 0.51)) == 1
@test Distributions.mode(Binomial(1, 0.49)) == 0
@test mode(Binomial(100, 0.4)) == 40
@test mode(Binomial(1, 0.51)) == 1
@test mode(Binomial(1, 0.49)) == 0
@test mode(Binomial(4, 2//3)) == 3
@test mode(Binomial(6, 2//7)) == 1
@test mode(Binomial(7, 1//8)) == 0

@test modes(Binomial(4, 2//3)) == [3]
@test modes(Binomial(5, 3//4)) == [4]
@test modes(Binomial(3, 2//4)) == [1, 2]
@test modes(Binomial(4, 2//5)) == [1, 2]
@test modes(Binomial(6, 2//7)) == [1, 2]
@test modes(Binomial(6, 3//7)) == [2, 3]
@test modes(Binomial(7, 1//8)) == [0, 1]

@test isplatykurtic(Bernoulli(0.5))
@test ismesokurtic(Normal(0.0, 1.0))
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