r - 如何计算属于某个值范围的数据点的百分比？

Question

给定一个值表（比如 0 到 100 之间）和附图，使用 R 计算有多少数据点落在值 20 到 60 之间（图像中的红色框）的最简单方法是什么？

有没有办法使用 R 的绘图功能创建那个红色框（我是使用图像编辑器完成的......）？

谢谢您的帮助。

Answer 1

要计算包含在区间内的概率质量：

x <- rnorm(1e6)  ## data forming your empirical distribution
ll <- -1.96      ## lower bound of interval of interest
ul <- 1.96       ## upper bound of interval of interest

sum(x > ll & x < ul)/length(x)
# [1] 0.949735

---

然后绘制直方图和红色框：

h <- hist(x, breaks=100, plot=FALSE)       # Calculate but don't plot histogram
maxct <- max(h$counts)                     # Extract height of the tallest bar
## Or, if you want the height of the tallest bar within the interval
# start <- findInterval(ll, h$breaks)
# end   <- findInterval(ul, h$breaks)
# maxct <- max(h$counts[start:end])

plot(h, ylim=c(0, 1.05*maxct), col="blue") # Plot, leaving a bit of space up top

rect(xleft = ll, ybottom = -0.02*maxct,    # Add box extending a bit above
     xright = ul, ytop = 1.02*maxct,       # and a bit below the bars
     border = "red", lwd = 2)

Answer 2

set.seed(42) 
x <- rlnorm(5000) #some data
hist(x) #histogram
rect(7,-50,10,100,border="red") #red rectangle
table(cut(x,breaks=c(0,7,10,Inf)))/length(x) #fraction of values in intervals
#(0,7]    (7,10]   (10,Inf] 
#0.9754   0.0136   0.0110 

Cut根据它们所属的区间对值进行分类。table然后创建一个计数表，然后可以将其除以总计数length(x)。