# [R] medians on data frame with duplicated rows

Date: Wed, 02 Apr 2008 11:50:23 -0500

Dear list:

I have a data frame with student name, class he attended and marks for subjects he attended.
Students took second exam if they performed badly in their first attempt. I want to consider the test scores where they obtain highest median.

there are 6 classes. As a sample case, I will consider only classes A, B and C.

For class A, Student Raj took first exam and he did not score well. He re-took his exam and scored well. his median marks second time was high, and thus I will consider
only marks he scored second time. Similarly, for class A ,kiran took one class and I have no choice but to consider his marks in his only attempt.

Matt took class B and performed poorly. In his second attempt, he scored well and thus I will consider his second attempt because his median his high.

Since only one student took class C and took exam only once, I will consider Ram's test scores for the class he took.

Name
Class
Trigno
Algebra
Calculus
Sci.Comp
CS
Raj
A
10
20
12
24
20
Raj
A
20
21
25
25
25
Kiran
A
20
24
24
23
24
Matt
B
12
10
13
9
9
Matt
B
20
24
23
22
24
Ram
C
25
25
25
25
25
Rhea
D
21
12
12
21
23
Jack
E
12
15
16
18
19
Smita
F
13
18
19
19
20
> rtest

Name Class Trigno Algebra Calculus Sci.Comp CS

```1   Raj     A     10      20       12       24 20
2   Raj     A     20      21       25       25 25
3 Kiran     A     20      24       24       23 24
4  Matt     B     12      10       13        9  9
5  Matt     B     20      24       23       22 24
6   Ram     C     25      25       25       25 25
7  Rhea     D     21      12       12       21 23
8  Jack     E     12      15       16       18 19
9 Smita     F     13      18       19       19 20

```

I want to write a small loop program that would give me back a data frame.

>tclass <- c('A','B','C')
> tclass
 "A" "B" "C"

> for(i in 1:length(tclass)){
+ k = rtest[rtest\$Class==tclass[i],]
+ if(nrow(k)>1){
+ x <- k[,c(-1,-2)]
+ rownames(x) <- k[,1]
+ k2 = apply(x,1,median)
+ fin_dat <- c(rtest\$Name==max(names(k2)),)}
+ else{
+ fin_dat <- c(k)
+ }
+ }

Error in `row.names<-.data.frame`(`*tmp*`, value = c(4L, 4L, 2L)) :   duplicate 'row.names' are not allowed

my code:

for(i in 1:length(tclass)){

k = rtest[rtest\$Class==tclass[i],] # selecting all students who took that class

``` if(nrow(k)>1){                           # if there are many students
then...
x <- k[,c(-1,-2)]                         # take only their scores
and leave their name and class column
rownames(x) <- k[,1]              # to choose row of scores for a student
```
with high median, I am making row names and since the student names are duplicated.. I am having problem
k2 = apply(x,1,median) # obtain median  fin_dat <- c(rtest\$Name==max(names(k2)),)} # get test scores line from original data frame and write back to fin_dat object
``` else{                                   # if a student took only once his
exam
fin_dat <- c(k)                   # write his score to fin_dat
```
}
}

Could any one please help me here with my problem. Since Raj is duplicated, I am having this error. If there is a better way of doing this, I appreciate your help.

Thanks