Issue with sample() in R

Question

Pretty simple question. I am trying to sample 20 numbers (with replacement) from the first 10 natural numbers.

This

sample(x = 1:10, size = 0.2*100, replace = TRUE) %>% length

gives 20 (and works), but

sample(x = 1:10, size = (1-0.8)*100, replace = TRUE) %>% length

gives 19.

I can always do

sample(x = 1:10, size = (100 - 0.8*100), replace = TRUE) %>% length

(that works fine and shows 20), but I'm curious why having it in parenthesis doesn't work.

score 1 · Answer 1 · answered Jun 28 '20 at 03:31

1

It is because the value is not exactly equal to 20 in size. We can either round or use ceiling

sample(x = 1:10, size = ceiling((1-0.8)*100), replace = TRUE) %>% length
#[1] 20

20 - (1-0.8)*100
#[1] 3.552714e-15

answered Jun 28 '20 at 03:31

akrun

I understand, but I need to be able get `20` when I pass `0.8` and `19` when I pass `0.81` – wrahool Jun 28 '20 at 03:37
1

@wrahool these are floating point and there is precision involved in it. So, it is not going to be an exact value – akrun Jun 28 '20 at 03:40
1

wouldn't round be better than ceiling in this case? – rawr Jun 28 '20 at 04:38
Please read FAQ 7.31. This will help answer you questions about floating point numbers. – Retired Data Munger Jun 28 '20 at 17:57

1 Answers1