Applying "dim" function over elements of a list in R

Question

I have n number of lists, lets say list1, list2, ..., listn. Each list has 10 elements and I need to calculate the "mean" of "dim" of ten elements of each list. So the output should be a vector of length n.

For example the first element of the output vector should be:

n1 = mean(dim(list1[[1]]), dim(list1[[2]]), dim(list1[[3]]), ..., dim(list1[[10]]) 

I know how to obtain it using for-loops but I am sure it is not the best solution.

The lists have structure derived from one of "Bioconductor" R packages called "edgeR". So each element of the list has this structure:

 $ :Formal class 'TopTags' [package "edgeR"] with 1 slots
  .. ..@ .Data:List of 4
  .. .. ..$ :'data.frame':      2608 obs. of  4 variables:
  .. .. .. ..$ logFC : num [1:2608] 6.37 -6.48 -5.72 -5.6 -4.01 ...
  .. .. .. ..$ logCPM: num [1:2608] 5.1 2.55 2.08 1.57 3.08 ...
  .. .. .. ..$ PValue: num [1:2608] 3.16e-292 1.57e-187 2.15e-152 5.58e-141 1.27e-135 ...
  .. .. .. ..$ FDR   : num [1:2608] 7.37e-288 1.83e-183 1.67e-148 3.25e-137 5.92e-132 ...
  .. .. ..$ : chr "BH"
  .. .. ..$ : chr [1:2] "healthy" "cancerous"
  .. .. ..$ : chr "exact"

And since each list has 10 elements, I have 10 repeats of above structure when running:

str(list1)

Answer 1

Original question

lapply (or sapply) is your friend:

mean(sapply(mylist,dim))

If you have many lists with a uniform meaning and structure, you should use instead a list of lists (i.e., mylist[[3]] instead of mylist3).

Edited question

sapply(mylist, function(x) mean(sapply(x,dim)))

will return a vector of means of inner lists.

Question in a comment

If your list contains matrices instead of vectors and you want to average one of the dimensions (dim(.)[1] or dim(.)[2]), you can use ncol and nrow for that instead of dim.

Alternatively, you can pass any function there, e.g.,

sapply(mylist, function(x) mean(sapply(x, function(y) sum(dim(y)))))

to average the sums of dimensions.