Easy question with probability

2011 12 7
2 个回答
回答已采纳
更新时间：2017 3 18
6 次查看（30 天）

0 个投票

Hi,
Let's say
P = [0.1 0.3 0.4 0.2]
X = [1 2 3 4]
where P(n) is the probability to select the X(n) element. I wish to make a function that select an "random" element of X according to its probability, like
f = myfun(P,X)
>> f = 2
thx a lot

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 采纳的回答

Andrei Bobrov
Andrei Bobrov 2011-12-7

2 个投票

function F = myfun(P,X)
x = cumsum([0 P(:).'/sum(P(:))]);
x(end) = 1e3*eps + x(end);
[a a] = histc(rand,x);
F = X(a);

5 个评论
显示 3更早的评论 隐藏 3更早的评论

Steven
Steven 2011-12-7
it works perfect, but may you comment why this line:
x(end) = 1e3*eps + x(end);
Steven
Steven 2011-12-7
wait, should not it be F = X(a) instead ? in this case, probabily are not good...
Andrei Bobrov
Andrei Bobrov 2011-12-7
My typo! Corrected.
Oleg Komarov
Oleg Komarov 2011-12-7
Andrei's function should read:
function F = myfun(P,X)
p = cumsum([0; P(1:end-1).'; 1+1e3*eps]);
[a a] = histc(rand,p);
F = X(a);
Jyotshna Ramashire
Jyotshna Ramashire 2017-3-18
can you please explain the codes?

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更多回答（1 个）

Roger Stafford
Roger Stafford 2017-3-18

1 个投票

Also a little late, this also works:
C = cumsum(P);
f = X(1+sum(C(end)*rand>C));

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