R语言中density函数中kernel参数所对应的核函数视乎都具有拖尾，一下为box核的概率密度估算代码。

density_box=function(entity,bandwidth)

{

  if (missing(bandwidth)) {

    bandwidth=density(entity)$bw

  }

  min_x=min(entity)

  max_x=max(entity)

  x=seq(min_x, max_x,length.out=1000)

  y=rep(0, length(x))

  box=function(entity){

    for (i in 1:length(x)) {

      if (abs(x[i] - entity) <= bandwidth/2) {

        y[i] <<- y[i] + 1

      }

    }

  }

  for(i in 1:length(entity))

  {

    box(entity[i])

  }

  y=y/length(entity)

  result=cbind(x,y)

  colnames(result)=c("scale","density")

  result

}

y=density_box(entity)

par(mfrow = c(2, 1))

plot(y,type="l")

plot(density(entity))

以下为效果图，上图为box核，下图为高斯核