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I asked this question Pasting columns of matrix with a specific range in R and this method was suggested.

  g <- rep(1:2, each = 3)
  t(apply(a, 1, tapply, g, paste, collapse = " "))

Unfortunately this method is too slow, and I am looking for fast way and more flexible way.

In fact I am going to write it as a function in C++ if there is not any other way and call results to R.

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1 回答 1

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I've been using this function to paste columns of a data frame

pasteDFcol <- function(mydf,clmnnames=c("V1","V2"),sepChar=" "){
    do.call("paste",c(mydf[clmnnames],sep=sepChar))
}

You can pass your matrix using as.data.frame, and specify which columns you want to join, e.g.

a=matrix(1:600000,ncol=600)
a1.df <- data.frame(V1=pasteDFcol(as.data.frame(a),clmnnames=paste0("V",1:300)),
              V2=pasteDFcol(as.data.frame(a),clmnnames=paste0("V",301:600)))
a2 <- as.matrix(a1.df)

It is about twice as fast as the method you were using.

For pasting columns 1:4, 5:8... or any other rolling frame, lets modify the function to take starting column, and number of columns to be pasted as arguments, then use sapply.

pasteDFcol <- function(clmStart, clmNum=4, mydf, sepChar=" "){
    do.call("paste",c(mydf[paste0("V",clmStart:(clmStart+clmNum-1))],sep=sepChar))
}
a=matrix(1:400,ncol=40)
pasteDFcol(clmStart=1, clmNum=4,mydf=as.data.frame(a))
a1 <- sapply(seq(1, 40, by=4), pasteDFcol, clmNum=4, mydf=as.data.frame(a))
于 2013-11-08T02:34:49.513 回答