[R] More efficient option to append()?

[Alex Ruiz Euler]

Daniel,

it works, thanks for your time with this simple matter.

Best,
Alex

On Wed, 17 Aug 2011 16:35:48 -0700
"Daniel Nordlund" <djnordlund at frontier.com> wrote:

> 
> > -----Original Message-----
> > From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-project.org]
> > On Behalf Of Alex Ruiz Euler
> > Sent: Wednesday, August 17, 2011 3:54 PM
> > To: r-help at r-project.org
> > Subject: [R] More efficient option to append()?
> > 
> > 
> > Dear R community,
> > 
> > I have a 2 million by 2 matrix that looks like this:
> > 
> > x<-sample(1:15,2000000, replace=T)
> > y<-sample(1:10*1000, 2000000, replace=T)
> >       x     y
> > [1,] 10  4000
> > [2,]  3  1000
> > [3,]  3  4000
> > [4,]  8  6000
> > [5,]  2  9000
> > [6,]  3  8000
> > [7,]  2 10000
> > (...)
> > 
> > 
> > The first column is a population expansion factor for the number in the
> > second column (household income). I want to expand the second column
> > with the first so that I end up with a vector beginning with 10
> > observations of 4000, then 3 observations of 1000 and so on. In my mind
> > the natural approach would be to create a NULL vector and append the
> > expansions:
> > 
> > myvar<-NULL
> > myvar<-append(myvar, replicate(x[1],y[1]), 1)
> > 
> > for (i in 2:length(x)) {
> > myvar<-append(myvar,replicate(x[i],y[i]),sum(x[1:i])+1)
> > }
> > 
> > to end with a vector of sum(x), which in my real database corresponds
> > to 22 million observations.
> > 
> > This works fine --if I only run it for the first, say, 1000
> > observations. If I try to perform this on all 2 million observations
> > it takes long, way too long for this to be useful (I left it running
> > 11 hours yesterday to no avail).
> > 
> > 
> > I know R performs well with operations on relatively large vectors. Why
> > is this so inefficient? And what would be the smart way to do this?
> > 
> > Thanks in advance.
> > Alex
> > 
> 
> Alex, 
> 
> does the following do what you want?
> 
> myvar <- rep(y,x)
> 
> Hope this is helpful,
> 
> Dan
> 
> Daniel Nordlund
> Bothell, WA USA
> 
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