Question

I’ve got a list of lists of bootstrap statistics from a function that I wrote in R. The main list has the 1000 bootstrap iterations. Each element within the list is itself a list of three things, including fitted values for each of the four variables (“fvboot” — a 501×4 matrix).

I want to make a vector of the values for each position on the grid of x values, from 1:501, and for each variable, from 1:4.

For example, for the ith point on the xgrid of the jth variable, I want to make a vector like the following:

        vec = bootfits$fvboot[[1:1000]][i,j]

but when I do this, I get:

recursive indexing failed at level 2

googling around, i think I understand why R is doing this. but I’m not getting an answer for how I can get the ijth element of each fvboot matrix into a 1000×1 vector.

help would be much appreciated.

Answer 1

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.