Extract just the number

General
1

I would like to know how do I extract just the number 4? Sorry if the question is simple

> a<-subset(a, data ==datas & category == chosse, select="PCP")
> a
# A tibble: 1 x 1
    PCP
  <dbl>
1     4
2

use a$PCP?

I am not sure whether I understand your question clearly.