将数据框变量重塑为列表

Question

I'm havin an issue with R.

I have the following dataframe:

FirstName LastName Exercice1 Exercice2
   Eric       A        15        12
   Eric       A        14        14
   Eric       A        12        15
   Paul       B        12        14
   Paul       B        14        14
   Joe        C        15        12
   Joe        C        15        17
   Joe        C        16        17
   Joe        C        18        19

And I want to change it into the following:

FirstName   LastName            Mark
                         Exercice1 Exercice2
   Eric         A            15        12
                             14        14
                             12        15
                         Exercice1 Exercice2
   Paul        B             12        14
                             14        14
                         Exercice1 Exercice2
   Joe        C              15        12
                             15        17
                             16        17
                             18        19

In short I would like to group for each students their marks for every test into a single variable that is a data frame.

Do you have any ideas if that is possible and how I should do?

Answer 1

If all you need is the Mark column to be a data.frame of the student, then you can use this:

dat <- read.table(text = "FirstName LastName Exercice1 Exercice2
   Eric       A        15        12
                  Eric       A        14        14
                  Eric       A        12        15
                  Paul       B        12        14
                  Paul       B        14        14
                  Joe        C        15        12
                  Joe        C        15        17
                  Joe        C        16        17
                  Joe        C        18        19", stringsAsFactors = FALSE, header = TRUE)

dat2 <- dat[!duplicated(dat[,1:2]),1:2]
dat2$Mark <- I(split(dat[,3:4], list(dat$FirstName, dat$LastName), drop = TRUE))

dat2
#  FirstName LastName         Mark
#1      Eric        A c(15, 14....
#4      Paul        B c(12, 14....
#6       Joe        C c(15, 15....

Mark is a list of dataframes:

> dat2$Mark
$Eric.A
  Exercice1 Exercice2
1        15        12
2        14        14
3        12        15

$Paul.B
  Exercice1 Exercice2
4        12        14
5        14        14

$Joe.C
  Exercice1 Exercice2
6        15        12
7        15        17
8        16        17
9        18        19

Now in order to print like you showed you'd need a custom print function, but you shouldn't need that anyway. Or just add empty rows to get your desired print output. This isn't pretty nor like your output, but it's a start:

dat3 <- dat
dat3[duplicated(dat[,1:2]),1:2] <- ""
print(dat3, row.names = FALSE)
# FirstName LastName Exercice1 Exercice2
#      Eric        A        15        12
#                           14        14
#                           12        15
#      Paul        B        12        14
#                           14        14
#       Joe        C        15        12
#                           15        17
#                           16        17
#                           18        19