R get() function error

Question

I\'m trying to populate a set of matrices where the matrix (object) names are held in a list. I can use the get() to return the object with the given name, but I\'m running

Answer 1

This is addressed in FAQ 7.21. The most important part of that FAQ is the end where it says to use a list (a real list, not the vector that you are calling a list above). A lot of things become much easier if you have a list of matricies instead of a bunch of matricies in your global work space. Here is an example:

mnames <- c('m.1','m.2','m.3')
m.1 <- matrix(1, 2, 2)
m.2 <- matrix(2, 2, 2)
m.3 <- matrix(3, 2, 2)

## put matricies into a list
mymats <- lapply( mnames, get )
names(mymats) <- mnames

## change 1 value in each matrix a different way
mymats[['m.2']][1,1] <- 22
mymats[[1]][2,2] <- 11
tmp <- "m.3"
mymats[[tmp]][1,2] <- 33

## change the same element in each matrix using a loop
for( i in seq_along(mymats) ) {
 mymats[[i]][2,1] <- 44
}

## apply the same function to every matrix and simplify the output
sapply( mymats, rowMeans )

This is much simpler than messing around with get and assign.

Answer 2

Use function assign instead of get:

assign(list.names[1],c(1,2,3,4))

get returns an object's value, assign assigns. :)

Same thing with eval, it just evaluates your call.