Making a vector from list elements in R

Use unlist() function in R. From example(unlist),

unlist(options())
unlist(options(), use.names = FALSE)

l.ex <- list(a = list(1:5, LETTERS[1:5]), b = "Z", c = NA)
unlist(l.ex, recursive = FALSE)
unlist(l.ex, recursive = TRUE)

l1 <- list(a = "a", b = 2, c = pi+2i)
unlist(l1) # a character vector
l2 <- list(a = "a", b = as.name("b"), c = pi+2i)
unlist(l2) # remains a list

ll <- list(as.name("sinc"), quote( a + b ), 1:10, letters, expression(1+x))
utils::str(ll)
for(x in ll)
  stopifnot(identical(x, unlist(x)))

You can extract one vector at a time using sapply, e.g. for i=1 and j=1:

i <- 1
j <- 1
vec <- sapply(bootfits, function(x){x$fvboot[i,j]})

sapply carries out the function (in this case an inline function we have written) to each element of the list bootfits, and simplifies the result if possible (i.e. converts it from a list to a vector).

To extract a whole set of values as a matrix (e.g. over all the i's) you can wrap this in another sapply, but this time over the i's for a specified j:

j <- 1
mymatrix <- sapply(1:501, function(i){
    sapply(bootfits, function(x){x$fvboot[i,j]})
})

Warning: I haven't tested this code but I think it should work.

This would be easier if you give a minimal example object. In general, you can not index lists with vectors like [[1:1000]]. I would use the plyr functions. This should do it (although I haven't tested it):

require("plyr")
laply(bootfits$fvboot,function(l) l[i,j])

If you are not familiar with plyr: I always found Hadley Wickham's article 'The split-apply-combine strategy for data analysis' very useful.