selecting a random element from vector and ... in matlab

Question

Jack Ie 2016-4-2

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此问题的直接链接

https://ww2.mathworks.cn/matlabcentral/answers/276777-selecting-a-random-element-from-vector-and-in-matlab

评论： Walter Roberson 2016-4-5

采纳的回答： Walter Roberson

I have 3 problem in matlab:

selecting a random element from vector with probability proportional to the occurrence frequency of this element in the vector?
selecting the most popular element from vector(the most occurrence frequency of this element in the vector)?
converting a vector into a probability distribution of elements.If the probability of seeing a particular element is less than a given threshold r=0.5, this element is deleted from vector.

Thanks a lot.

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Answer 1

Walter Roberson 2016-4-2

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https://ww2.mathworks.cn/matlabcentral/answers/276777-selecting-a-random-element-from-vector-and-in-matlab#answer_216138

在 MATLAB Online 中打开

For the first one see http://www.mathworks.com/help/stats/randsample.html . Just submit the vector as the population, and since the population will be chosen from uniformly randomly, the probability that any particular value will be chosen will depend upon how frequently it occurs relative to the other values.

For the second one, see http://www.mathworks.com/help/matlab/ref/mode.html

For the third one:

[uniquepop, ~, popidx] = unique(ThePopulation);
counts = histc(popidx, 1:length(uniquepop));
selected_elements = uniquepop( find(counts ./ length(ThePopulation) >= r ) );

Note: with r = 0.5, selected_elements may have 0, 1, or 2 entries.

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Jack Ie 2016-4-3

Thanks a lot Walter. for the first problem when vector has one element, result of randsample is not correct. it return random number from 1 to that element. for example: n=[3]; x = randsample(n,1); x=1 or x=2 or x=3 but I want x=3