[R] melting a data frame

[arun]

Hi,

You could try:
set.seed(48)
dat1<- as.data.frame(matrix(sample(1:40,189*130,replace=TRUE),ncol=189))
res<-do.call(rbind,lapply(split(colnames(dat1),((seq_len(ncol(dat1))-1)%/%21)+1),function(x) {x1<- dat1[,x]; colnames(x1)<- paste("V",1:21);x1}))
 row.names(res)<- 1:nrow(res)
 dim(res)
#[1] 1170   21
A.K.



----- Original Message -----
From: Data Analytics Corp. <walt at dataanalyticscorp.com>
To: R help <r-help at r-project.org>
Cc: 
Sent: Saturday, September 7, 2013 11:33 PM
Subject: [R] melting a data frame

Hi,

Suppose I have a data frame with 189 columns.  The columns are actually 9 blocks of 21 columns each, each block representing measures on each of 9 products.  There are 130 rows.  Suppose I extract the first block of 21 columns and make them into a separate data frame.  I then want to take the second block of 21 columns and rbind it to the first; then the third set of 21 and rbind it to the first two; etc.  The final data frame should have 1170 (= 9 * 130)  rows and 21 columns.  Is there an easy way to melt the blocks comparable to using the melt function in the plyr package (which is why I'm referring to what I want to do as "melting")?  It seems that there should be a simple way to do this.  I used a for loop which worked, but I want to see if there's a more efficient way.

Thanks,

Walt

________________________

Walter R. Paczkowski, Ph.D.
Data Analytics Corp.
44 Hamilton Lane
Plainsboro, NJ 08536
________________________
(V) 609-936-8999
(F) 609-936-3733
walt at dataanalyticscorp.com
www.dataanalyticscorp.com

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