# [R] how to extract the row names of a matrix using for loop or other looping

From: peter eric <eric_wzl_at_yahoo.com>
Date: Sun 11 Dec 2005 - 04:17:47 EST

Hi all,
I have a matrix and its cluster...and i like to extract the row names of each cluster....but using the for loop or some other looping

a<-matrix(c(seq(3,45,3),seq(10,6,-1)),4,5,byrow=F)  col<-c("ra","rb","rc","rd","re")
rows<-c("ca","cb","cc","cd")
dimnames(a)<-list(rows,col)

```a                                ##        matrix
#-----------------------------------------------------------------------------------
#      ra rb rc rd re
```

# ca 3 15 27 39 9
# cb 6 18 30 42 8
# cc 9 21 33 45 7
# cd 12 24 36 10 6

```t<-list()                        ## clusters of the matrix
```
s<-list()
r<-c(1:3)
for(i in 1:3)
{ p<-seq(r[i],4,3)
s[[i]]<-print(p)
t[[i]]<-a[s[[i]],,drop=FALSE]
}
print(t)

##[]
ra rb rc rd re
ca 3 15 27 39 9
cd 12 24 36 10 6
[]
ra rb rc rd re
cb 6 18 30 42 8
[]
ra rb rc rd re
cc 9 21 33 45 7

##now if i want to extract the row names i can do it manually giving the values like

rowc <- list(c(rownames(t[])), c(rownames(t[])), rownames(t[]))

but i like to do using for loop or other loops...could you give me some suggestion..iÇve tried like this..but it is not working....

rowc<-list(for(i in 1:3){p<-c();k<-rownames(t[[i]]);p[[i]]<-print(k)})

## here IÇm getting only the final rowname t[]..other two values are missing..how could i do this to store all the values...........

thank you...

with regards,
eric.

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