如何在R中找到概率 [英] How to find probability in R

问题描述

如何在 R 中的 sample 命令中使用 prob 参数，以便它也涵盖条件概率?例如字母表中的字母:生成字母b"的概率取决于前一个生成的字母.

How could you use the prob argument in the sample command in R so that it covers conditional probability as well? For example, the letters of the alphabet: the probability of generating the letter 'b' depends on the previous letter generated.

谢谢！

推荐答案

这个问题还是有点难回答，如果你指定一个条件概率的例子会有帮助，另见 此处.

The question is still a bit difficult to answer, it would help if you specified an example of the conditional probability, seealso here.

但是如果我们假设我们有a、b和c，并且a和b很可能出现在彼此之后，我们可以继续从这里，和我们可以修改函数如下:

But if we assume that we have a,b, and c, and a and b have a high probability of occuring after eachother, we can continue on the answer from here, and we could modify the function as follows:

# n = number of elements
# sample_from = draw random numbers from this range
random_non_consecutive <- function(n=10,sample_from = seq(1,5))
{
  y= rep(NA, n)
  prev=-1 # change this if -1 is in your range, to e.g. max(sample_from)+1
  probs = rep(1,length(sample_from));names(probs)=sample_from
  for(i in seq(n)){

    # your conditional probability rules should go here.
    if(prev=="a")
    {
      probs = c('a'=0,'b'=0.9,'c'=0.1)
    }
    if(prev=="b")
    {
      probs = c('a'=0.9,'b'=0,'c'=0.1)
    }
    if(prev=="c")
    {
      probs = c('a'=0.9,'b'=0.1 ,'c'=0)
    }

    y[i]=sample(setdiff(sample_from,prev),1,prob = probs[names(probs) %in% setdiff(sample_from,prev)])
    prev = y[i]
  }
  return(y)
}

在这种情况下，a 和 b 出现的概率很高.事实上:

In this case, a and b have a high probability of occuring after eachother. And indeed:

random_non_consecutive(40,letters[1:3])
 [1] "c" "a" "b" "a" "b" "a" "b" "c" "b" "a" "b" "a" "b" "a" "b" "a" "b" "a" "b" "a" "b" "a" "b" "a" "c" "a" "b" "a" "b" "c" "a" "b" "a" "b" "a" "b" "a" "b" "a" "c"

希望这会有所帮助.

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