Re: [R] Efficient way to use data frame of indices to initialize matrix

2010-12-08 Thread Cutler, Gene
Sent: Tuesday, December 07, 2010 11:00 AM > To: Greg Snow > Cc: Gene; r-help@r-project.org > Subject: Re: [R] Efficient way to use data frame of indices to > initialize matrix > > > On Dec 7, 2010, at 1:49 PM, Greg Snow wrote: > > > tmpdf <- data.frame( x = c(

Re: [R] Efficient way to use data frame of indices to initialize matrix

2010-12-07 Thread David Winsemius
On Dec 7, 2010, at 1:49 PM, Greg Snow wrote: tmpdf <- data.frame( x = c(1,2,3), y=c(2,3,1), a=c(10,20,30) ) mymat <- matrix(0, ncol=3, nrow=3) mymat[ as.matrix(tmpdf[,c('x','y')]) ] <- tmpdf$a cbind is also useful for assembly of arguments to the matrix-`[<-` function: tmpdf <- data.fram

Re: [R] Efficient way to use data frame of indices to initialize matrix

2010-12-07 Thread Greg Snow
tmpdf <- data.frame( x = c(1,2,3), y=c(2,3,1), a=c(10,20,30) ) mymat <- matrix(0, ncol=3, nrow=3) mymat[ as.matrix(tmpdf[,c('x','y')]) ] <- tmpdf$a -- Gregory (Greg) L. Snow Ph.D. Statistical Data Center Intermountain Healthcare greg.s...@imail.org 801.408.8111 > -Original Message- > F

Re: [R] Efficient way to use data frame of indices to initialize matrix

2010-12-07 Thread Whit Armstrong
index m as a vector and do the assignment in one step i <- df$row + (df$col-1)*nrow(m) m[i] <- df$a or something along those lines. -Whit On Tue, Dec 7, 2010 at 1:31 PM, Cutler, Gene wrote: > I have a data frame with three columns, x, y, and a.  I want to create a > matrix from these values