[R] Basic question about re-writing for loop as a function

[Jim Holtman]

use Rprof to see where thr time is spent.

take the strsplit out of the loop and do it once outsidr to create an object you can test against in the loop.

you can probably get rid of the loop easily, but since there is no example of the data, it is hard to create a solution.


Sent from my iPad

On Aug 29, 2011, at 9:55, Chris Beeley <chris.beeley at gmail.com> wrote:

> Hello-
> 
> Sorry to ask a basic question, but I've spent many hours on this now
> and seem to be missing something.
> 
> I have a loop that looks like this:
> 
>    mainmat=data.frame(matrix(data=0, ncol=92, nrow=length(predata$Words_MH)))
> 
>    for(i in 1:length(predata$Words_MH)){
>    for(j in 1:92){
> 
>    mainmat[i,j]=ifelse(j %in%
> as.numeric(unlist(strsplit(predata$Words_MH[i], split=","))), 1, 0)
> 
>    }
>    }
> 
> What it's doing is creating a matrix with 92 columns, that's the
> number of different codes, and then for every row of my data it looks
> to see if the code (code 1, code 2, etc.) is in the string and if it
> is, returns a 1 in the relevant column (column 1 for code 1, column 2
> for code 2, etc.)
> 
> There are 1000 rows in the database, and I have to run several
> versions of this code, so it just takes way too long, I have been
> trying to rewrite using lapply. I tried this:
> 
>    myfunction=function(x, y) ifelse(x %in%
> as.numeric(unlist(strsplit(predata$Words_MH[y], split=","))), 1, 0)
> 
>    for(j in 1:92){
>    mainmat[,j]= lapply(predata$Words, myfunction)
>    }
> 
> but I don't think I can use something that takes two inputs, and I
> can't seem to remove either.
> 
> Here's a dput of the first 10 rows of the variable in case that's helpful:
> 
> predata$Words=c("1", "1", "1", "1", "2,3,4", "5", "1", "1", "6", "7,8,9,10")
> 
> Given these data, I want the function to return, for the first column,
> 1, 1, 1, 1, 0, 0, 1, 1, 0, 0 (because those are the values of Words
> which contain a 1) and for the second column return 0, 0, 0, 0, 1, 0,
> 0, 0, 0, 0 (because the fifth value is the only one that contains a
> 2).
> 
> Any suggestions gratefully received!
> 
> Chris Beeley
> Institute of Mental Health, UK
> 
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