Question

I just started learning R programming and have few doubts about working on repeated values specifically in a single column of a data frame. For example consider a ‘Sample’ dataframe `

 > Sample
     id   time1   time2             user   group
21   21   21.7    16.1               A        1   
22   22   22.6    17.0               A        2   
23   23   20.9    16.2               A        3   
24   24   21.6    16.2               B        1  
25   25   22.2    16.9               B        1   
26   26   22.5    16.9               B        1 
27   27   22.2    17.3               B        2 
28   28   24.3    16.8               D        2
29   29   22.3    16.8               D        2 
30   30   22.6    17.0               E        3  
31   31   20.1    16.5               E        3  
32   32   22.0    16.9               E        3 
33   33   22.8    16.5               E        4   
34   34   22.0    17.0               E        4  
35   35   22.4    17.0               F        1   
36   36   22.3    16.3               F        1   
37   37   20.6    16.2               F        2   

Now I need to find
1) the user with highest average ‘time1’
2) the user belonging to ‘group’ 3 and having biggest ‘time2’

As of now my understanding is that I should use combination of repeated(), unique(), max() and mean() and NROW() functions. But I am having trouble trying to figure that out. Any pointers on how to approach?

Answer 1

You can use which.max and tapply:

1)

which.max(tapply(Sample$time1,Sample$user,mean))
D 
3

2)

which.max(tapply(Sample$time2,Sample$user,max))
B 
2 

Be careful of ties though.