Creating a List of 100 Binomial Distributed Values

General Usage
1

I want a list x it contain 1 and -1, if rand(Binomial(1,0.5),1)[1] == 1 is true the value in that position of x is 1 and if it is not true then the value is -1 . i need to do this for 100 many times, so my length of x should be 100 How do i do that?? Sorry for the inconvenience.
Thanks for any advice or help.

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Edit: deleting as the post question was rewritten and changed.

3

An easy way to do this is by scaling rand():

x = 2*rand(0:1, 100) .-1
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x = rand((-1, 1), 100)

?

3 Likes
5

BTW, this is needlessly complicated. You are creating a length-1 vector, and reading out the first element. It’s slow, too.

Instead, just directly generate a scalar value:

rand(Binomial(1,0.5))

Similarly, you can use rand(), not rand(1)[1].

5 Likes
6

Thanks for your help. It is working now.

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Generating rands from a range isn’t optimal. Here are some comparisons:

julia> @btime rand(0:1, 100);
  656.522 ns (1 allocation: 896 bytes)

julia> @btime rand((0, 1), 100);
  161.224 ns (1 allocation: 896 bytes)

julia> @btime rand(Bool, 100);
  48.485 ns (1 allocation: 160 bytes)

So the fastes solution here uses something almost like your suggestion, @chiion. It has slightly more allocations than rand((-1, 1), 100):

(rand(Bool, 100) .* 2) .- 1
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:+1:

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And don’t forget the similar:

(-1).^rand(Bool, 100)

which yields the same result but perhaps looks neater.

1 Like
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ok. Thanks