[R] "unsparse" a vector

[Sam Steingold]

To be clear, I can do that with nested for loops:

v <- c("A1B2","A3C4","B5","C6A7B8")
l <- strsplit(gsub("(.{2})","\\1,",v),",")
d <- data.frame(A=vector(length=4,mode="integer"),
                B=vector(length=4,mode="integer"),
                C=vector(length=4,mode="integer"))

for (i in 1:length(l)) {
  l1 <- l[[i]]
  for (j in 1:length(l1)) {
    d[[substring(l1[j],1,1)]][i] <- as.numeric(substring(l1[j],2,2))
  }
}


but I am afraid that handling 1,000,000 (=length(unlist(l))) strings in
a loop will kill me.


> * Sam Steingold <fqf at tah.bet> [2012-02-08 15:34:38 -0500]:
>
> Suppose I have a vector of strings:
> c("A1B2","A3C4","B5","C6A7B8")
> [1] "A1B2"   "A3C4"   "B5"     "C6A7B8"
> where each string is a sequence of <column><value> pairs
> (fixed width, in this example both value and name are 1 character, in
> reality the column name is 6 chars and value is 2 digits).
> I need to convert it to a data frame:
> data.frame(A=c(1,3,0,7),B=c(2,0,5,8),C=c(0,4,0,6))
>   A B C
> 1 1 2 0
> 2 3 0 4
> 3 0 5 0
> 4 7 8 6
>
> how do I do that?
> thanks.

-- 
Sam Steingold (http://sds.podval.org/) on Ubuntu 11.10 (oneiric) X 11.0.11004000
http://palestinefacts.org http://iris.org.il http://camera.org
http://ffii.org http://www.PetitionOnline.com/tap12009/
An elephant is a mouse with an operating system.