Reducing a data set

[Eric yang <yang_eric9@yahoo.com>]

 

Dear all,

 

I would like to know a fast way of reducing a data set based on certain conditions. For example, suppose I have the following data set

 

my.data <- data.frame(ID=c(rep("101-1", 10), rep("102-12", 14), rep("103-10", 3), rep("104-2", 8)), score=round(100*runif(35)))

 

> my.data

ID score

1 101-1 85

2 101-1 32

3 101-1 22

4 101-1 74

5 101-1 48

6 101-1 47

7 101-1 46

8 101-1 6

9 101-1 58

10 101-1 37

11 102-12 16

12 102-12 78

13 102-12 15

14 102-12 45

15 102-12 99

16 102-12 4

17 102-12 99

18 102-12 35

19 102-12 78

20 102-12 16

21 102-12 91

22 102-12 34

23 102-12 10

24 102-12 20

25 103-10 43

26 103-10 12

27 103-10 57

28 104-2 86

29 104-2 45

30 104-2 85

31 104-2 81

32 104-2 9

33 104-2 40

34 104-2 47

35 104-2 74

I would like to reduce the data set such that I have at most the top 5 scores for each ID number. Thus, I would end up with the following data set:

1 101-1 85

4 101-1 74

5 101-1 48

6 101-1 47

9 101-1 58

12 102-12 78

15 102-12 99

17 102-12 99

19 102-12 78

21 102-12 91

25 103-10 43

26 103-10 12

27 103-10 57

28 104-2 86

30 104-2 85

31 104-2 81

34 104-2 47

35 104-2 74

Thanks for any help in advance.

 

Regards,

Eric

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