filter id in cluster according another variable in R

Question

I have a data with 100 patients and each patient has values from 7 days (1 to 7). How can I select only patients according another variable only in day 1?

df <         


        

Answer 1

You can use the subset function in base R:

subset(df,RRT==0&day==1)

if you only need the id column the you can select

with(df,id[RRT==0&day==1])

Answer 2

When using dplyr:

library(dplyr)
df %>% 
  group_by(id) %>% 
  filter(day == 1 & RRT == 0) %>% 
  select(id)

or base R:

df[df$day == 1 & df$RRT ==0,"id"]