Converting a data frame with values into a matrix/

 > xy

Perhaps in this case:

noquote(with(xx, tapply(NES, list(Class, Name),
paste)))


On 12/03/2008, Srinivas Iyyer
<srini_iyyer_bio at yahoo.com> wrote:

Dear Group,
 I have a data frame like the following:


 x <- c("Mike","A",0.01)
 x1 <- c("Carl","A",0.2)
 x2 <- c("Gene","C",0.3)
 x3 <- c("James","A",-0.3)
 x4 <- c("Dough","B",0)
 xx <- rbind(x,x1,x2,x3,x4)
 colnames(xx)<-c("Name","Class","NES")
 xx <-as.data.frame(xx)

 > xx

    Name Class  NES
 x   Mike     A 0.01
 x1  Carl     A  0.2
 x2  Gene     C  0.3
 x3 James     A -0.3
 x4 Dough     B    0


 Now I want to create a matrix with unique xx$Name

on

 columns and unique xx$Class as rows.  I want to

fill

 my choice of values (in this case 1) if data

point not

 available.


 xy <-

 colnames(xy)<-unique(xx[,1])
 rownames(xy)<-unique(xx$Class)

 > xy

  Mike Carl Gene James Dough
 A    1    1    1     1     1
 C    1    1    1     1     1
 B    1    1    1     1     1





 I would love to have :

  Mike Carl Gene James Dough
 A    0.01    0.2    1     -0.3     1
 C    1    1    1     0.3     1
 B    1    1    1     1    0




 If I am not wrong this is called contigency or
 frequeny table.

 I tried xtabs on this.

 > z <- xtabs(NES ~ Name+Class,data=xx)

 Error in Summary.factor(4L, na.rm = FALSE) :
  sum not meaningful for factors


 I tried on other data frames, it worked. BUT the
 problem is it gives me 0.0000 even a value is not
 available for that row and column.  So if I have

data

 -0.00 it is considered 0.

 I tried. drop.unused.levels = T, I did not get

what I

 want. I want all row.col values not available to

be 1.

 Is there any other trick where I map by row and

column

 names instead of using advanced xtabs.

 thanks
 Srini