let's assume I have a dataset similar to this:
df1 <- data.frame(age==1:10, year==2004)
df2 <- data.frame(age==1:10, year==2005)
df3 <- data.frame(age==1:10, year==2006)
df <- rbind(df1,df2,df3)
df <- df %>% mutate(group=case_when(age %in% c(1:3) & year==2004 ~ "A"))
I want those who are 2, 3 and 4 years old in 2005 to be in group A, and those who are 3, 4 and 5 years old in 2006 to be in group A. How do I do this using a for-loop?
You can use ifelse here instead of a for loop. If I understand you correctly, you want anyone born between 2001 and 2003 to be group A, in which case you can do
df %>% mutate(group = ifelse((year - age) %in% 2001:2003, 'A', 'Not A'))
#> age year group
#> 1 1 2004 A
#> 2 2 2004 A
#> 3 3 2004 A
#> 4 4 2004 Not A
#> 5 5 2004 Not A
#> 6 6 2004 Not A
#> 7 7 2004 Not A
#> 8 8 2004 Not A
#> 9 9 2004 Not A
#> 10 10 2004 Not A
#> 11 1 2005 Not A
#> 12 2 2005 A
#> 13 3 2005 A
#> 14 4 2005 A
#> 15 5 2005 Not A
#> 16 6 2005 Not A
#> 17 7 2005 Not A
#> 18 8 2005 Not A
#> 19 9 2005 Not A
#> 20 10 2005 Not A
#> 21 1 2006 Not A
#> 22 2 2006 Not A
#> 23 3 2006 A
#> 24 4 2006 A
#> 25 5 2006 A
#> 26 6 2006 Not A
#> 27 7 2006 Not A
#> 28 8 2006 Not A
#> 29 9 2006 Not A
#> 30 10 2006 Not A
Created on 2022-10-08 with reprex v2.0.2