[Rcpp-devel] Joining each row of CharacterMatrix to return a CharacterVector?
hickey at wehi.EDU.AU
hickey at wehi.EDU.AU
Mon Dec 10 23:43:13 CET 2012
I preface this by stating that I'm very much a Rcpp beginner who is comfortable in R but I've never before used C++. I'm working through the Rcpp documentation but haven't been able to answer my question.
I've written an Rcpp (v0.10.1) function f that takes as input a CharacterMatrix X. X has 20 million rows and 100 columns. For each row of X the function alters certain entries of that row according to rules governed by some other input variables. f returns the updated version of X. This function works as I'd like it to:
# a toy example with nrow = 2, ncol = 2
> X <- matrix('A', ncol = 2, nrow = 2)
> X
[,1] [,2]
[1,] "A" "A"
[2,] "A" "A"
> X <- f(X, other_input_variables)
> X
[,1] [,2]
[1,] "Z" "A"
[2,] "z" "A"
However, instead of f returning a CharacterMatrix as it currently does, I'd like to return a CharacterVector Y, where each element of Y is a "collapsed" row of the updated X.
I can achieve the desired result in R by using:
Y <- apply(X=X, MARGIN = 1, FUN = function(x){paste0(x, collapse = '')})
> Y
[1] "ZA" "zA"
but I wondered whether this "joining" is likely to be more efficiently performed within my function f? If so, how do I join the 100 individual character entries of a row of the CharacterMatrix X into a single string that will then comprise an element of the returned CharacterVector Y?
Many thanks,
Pete
--------------------------------
Peter Hickey,
PhD Student/Research Assistant,
Bioinformatics Division,
Walter and Eliza Hall Institute of Medical Research,
1G Royal Parade, Parkville, Vic 3052, Australia.
Ph: +613 9345 2324
hickey at wehi.edu.au
http://www.wehi.edu.au
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