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

You are after:

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

What went wrong

Two things:

1. abc < -0.5 & abc > 0.5 is asking for values less than -0.5 and greater than 0.5

2. However, you actually had: abc[abc<-0.5 & abc>0.5] This does something a bit different due to scoping. Let's pull it apart:

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

   Now let's look at abc

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

   You've changed the value of abc! This is because <- is the assignment operator. You have set abc equal to 0.5 & abc > 0.5. To avoid this, use spacing (as in my code).