r - How to calculate the amount of numbers inside a specific range

Question

I'm still having problems calculating numbers.

Trying to find the amount of numbers inside [-0.5 , 0.5] the first line, and the amount of numbers outside the same range in the second line.

I use abc = rnorm(100, mean=0, sd=1). So I have 100 numbers in total, but i only have 35 numbers inside the range, and 35 outside the range, that dosen't add up to 100.

length(abc[abc>=-0.5 & abc<=0.5])
[1] 35

length(abc[abc<-0.5 & abc>0.5])
[1] 35

Then I tried:

length(which(abc>=-0.5 & abc<=0.5))
[1] 40

length(which(abc<-0.5 & abc>0.5))
[1] 26

And it still doesn't add up to 100. What's wrong?

Answer 1

你在追求：

R> set.seed(1)
R> abc = rnorm(100, mean=0, sd=1)
R> length(abc[abc >= -0.5 & abc <= 0.5])
[1] 41
R> length(abc[abc < -0.5 | abc > 0.5])
[1] 59

什么地方出了错

两件事情：

1. abc < -0.5 & abc > 0.5要求小于 -0.5且大于 0.5的值

2. 但是，您实际上有：abc[abc<-0.5 & abc>0.5]由于范围界定，这会有所不同。让我们把它分开：

   R> abc[abc<-0.5 & abc>0.5]
    [1] 1.5953 0.7383 0.5758 1.5118 1.1249 0.9438 <snip>
   

   现在让我们看看abc

   R> abc
   [1] FALSE FALSE FALSE  TRUE FALSE FALSE FALSE  
   

   你改变了abc! 这是因为<-是赋值运算符。您已设置abc为0.5 & abc > 0.5。为避免这种情况，请使用间距（如我的代码中所示）。

Answer 2

当想要像这样在半径内外查找数字时，考虑绝对值会很有帮助，然后您只需进行一次比较：

length(abc[abs(abc)<=0.5])
[1] 41
length(abc[abs(abc)>0.5])
[1] 59

或者您可以在一行中使用cutand来完成：table

table(cut(abs(abc),c(-Inf,0.5,Inf)))

  (-Inf,0.5] (0.5,Inf] 
       41        59 

Answer 3

作为捷径，您也可以这样做：

set.seed(1)
abc <- rnorm(100, mean=0, sd=1)
sum(abc>=-0.5 & abc<=0.5)
# [1] 41
sum(abc< -0.5 | abc>0.5)
# [1] 59

这是有效的，因为sum将 TRUE 视为 1，将 FALSE 视为 0。

Answer 4

或者通过subset：

set.seed(1)
abc <- rnorm(100, mean=0, sd=1)

length(subset(abc, abc >= (-0.5) & abc <= 0.5))
[1] 41
length(subset(abc, abc < (-0.5) | abc > 0.5))
[1] 59