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add rand(::IntSet) #21960

Merged
merged 3 commits into from
May 30, 2017
Merged

add rand(::IntSet) #21960

merged 3 commits into from
May 30, 2017

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rfourquet
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@rfourquet rfourquet commented May 19, 2017

The second commit optimizes rand(::Dict) by using a RangeGenerator object, the speed-up seems to be roughly +50%.

@rfourquet rfourquet added the randomness Random number generation and the Random stdlib label May 19, 2017
@mbauman
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mbauman commented May 19, 2017

I'm not sure we're consistent enough about the max element of an IntSet for this to make sense. We've been treating it as an unbounded set.

@StefanKarpinski
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rand(::IntSet) should randomly select one of the values that's in the set and return it (if it doesn't do that, then we should change it). Why does that require having a defined upper bound on what could be put in an IntSet?

@rfourquet
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I also don't understand what the problem is with the "max element"... There is a well defined number of elements in an IntSet, with a well defined set a contained integers, so selecting randomly one of them doesn't look like a consistency problem.

@mbauman
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mbauman commented May 19, 2017

My apologies, I didn't look closely enough. I was somehow thinking rand!. This is indeed very reasonable.

@rfourquet
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Oh you remark make more sense now if you were thinking rand! !

@rfourquet
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I realized that the non-scalar methods (creating/filling arrays) were missing for Dict, Set, IntSet, so I added them.

@rfourquet
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Good to go?

base/random.jl Outdated
* a type: the set of values to pick from is then equivalent to `typemin(S):typemax(S)` for
integers (this is not applicable to `BigInt`), and to ``[0, 1)`` for floating point numbers;

`S` defaults to `Float64`.

```jldoctest
julia> srand(0); rand(Int, 2)
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I'm not sure whether srand(0) is needed here, for the doctests?

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I would think yes, since otherwise the results would be different every time.

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So I saw that it's also possible to use a julia-repl block instead of jldoctest. Could be cleaner...

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Downside of that is that they wont be tested. On the other hand, these functions might be fundamental enough that they wont change. julia-repl is fine IMO.

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Instead of srand in the doctest you can use a meta block: https://github.com/JuliaLang/julia/search?l=Markdown&q=meta&type=&utf8=%E2%9C%93

@rfourquet
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Rebased. I will merge soon if no more comments come.

while true
n = rand(r, rg)
@inbounds b = s.bits[n]
b && return n
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will this actually be uniform?

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I believe so, and this is how other uniform random functionality are implemented (rand on a range, on Dict, etc.). Basically pick uniformly one of the possible positions, and if it's not valid try again.

test/random.jl Outdated
a2 = rand(rng..., C, 2, 3) ::Array{T, 2}
a3 = rand!(rng..., Array{T}(5), C) ::Vector{T}
a4 = rand!(rng..., Array{T}(2, 3), C) ::Array{T, 2}
for a in [a0, a1..., a2...]
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why not also a3, a4?

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Good catch, looks like unintentional omission.

1339893410598768192
1575814717733606317

julia> rand(MersenneTwister(0), Dict(1=>2, 3=>4))
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If this is not a doctest perhaps the MersenneTwister(0) is unnecessary

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Ah yes right.

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Actually, I think I wanted to illustrate different combinations of arguments and show the use of an explicit RNG (and MersenneTwister is the most likely to be used, but doesn't accept for now no-argument), so I would rather keep it as is.

And change "dict" -> "collection" in the exception,
as it is also used from rand(::Set).
@rfourquet
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Rebased. Will merge when CI turns green again.

@rfourquet rfourquet merged commit 086d36b into master May 30, 2017
@rfourquet rfourquet deleted the rf/rand-IntSet branch May 30, 2017 11:14
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6 participants