bucketing values

19 次查看（过去 30 天）
Greg
Greg 2011-7-21
Hi
I have a vector of values from 0 to 1 representing probabilities
A = [0.8756 0.1185 0.0059]
How can i generate a random number using rand() and map it to a value in A without looping. I can;t see how i can do this with vectorisation or with the built in functions.
My aim is generate a random numbers so 87% of the time I choose A(1), 11% A(2), etc...
Thanks

请先登录，再回答此问题。

采纳的回答

Teja Muppirala
Teja Muppirala 2011-7-21
If you have the Statistics Toolbox installed, there is the built-in RANDSAMPLE command to do this.
A = [0.8756 0.1185 0.0059];
X = randsample(numel(A),5000,true, A); % X gets 5000 samples
tabulate(X)

更多回答（5 个）

Daniel Shub
Daniel Shub 2011-7-21
Assuming your array A is short ...
A = [0.8756 0.1185 0.0059]
x = rand(1e3, 1);
y(x < A(1)) = 'a';
y(x >= A(1) & x < A(2)) = 'b';
y(x >= A(2)) = 'c';
  2 个评论
Fangjun Jiang
Fangjun Jiang 2011-7-21
I think all the answers provided are along the same line. In your case, the A needs to be [0.87,0.98,1].
Daniel Shub
Daniel Shub 2011-7-21
You are correct. I was sloppy.

请先登录，再进行评论。

Sean de Wolski
Sean de Wolski 2011-7-21
Like this?
A = [0.8756 0.1185 0.0059]; %percentiles (must sum to 1
R = rand(1,1000); %random data
B = [11 17 19]; %sample data to extract A% of the time
[junk,Bin] = histc(R,[-inf cumsum(A)]); %find the bin
C = B(Bin) %extract
Fangjun Jiang
Fangjun Jiang 2011-7-21
Something like this:
A = [0.8756 0.1185 0.0059];
RandNum=rand(1000,1);
Index=2*ones(size(RandNum));
Index(RandNum<A(1))=1;
Index(RandNum>1-A(3))=3;
sum(Index==1)
sum(Index==2)
sum(Index==3)
ans =
892
ans =
102
ans =
6
close enough?
Greg
Greg 2011-7-21
Thanks for all the answser
I'm not sure which idea scales better as in general A[] will be of different sizes so I can't explicitly code for 3 items.
I'm fairly new to Matlab so any further pointers is much appreciated.
Thanks
  1 个评论
Sean de Wolski
Sean de Wolski 2011-7-21
Randsample and Histc are both automated for large/varying A.

请先登录，再进行评论。

Greg
Greg 2011-7-21
Thanks Teja
I have the Stats Toolbox so this looks to be exactly what i'm looking for. I will play around with this some more but so far so good
Cheers Greg

类别

在 Help Center 和 File Exchange 中查找有关 Noncentral t Distribution 的更多信息

标签

产品

Community Treasure Hunt

Find the treasures in MATLAB Central and discover how the community can help you!

Start Hunting!

Translated by