Matrix as element of a dataframe in R

Question

I have an lapply function that iterates over a list of elements. For each element, the result is a matrix. Based on the list of elements and the list of matrixes, I would like to return a list of dataframes of the form

element1, matrix1
element2, matrix2
...
...
elementn, matrixn

Example:

e <- list(1,2)
r <- lapply(e, function(x) matrix(ncol = x, nrow = x))

I would like to get a list with these elements

(1, matrix(1x1))
(2, matrix(2x2))

Answer 1

You can construct data frames in the lapply function, with I(list(...)) which can wrap the matrix as one element in the data frame:

r <- lapply(e, function(x) data.frame(element = x, mat = I(list(matrix(ncol = x, nrow = x)))))

This gives a list of data frames:

r
# [[1]]
#   element mat
# 1       1  NA

# [[2]]
#   element          mat
# 1       2 NA, NA, ....

You can rbind the result together with do.call(rbind, ...) :

do.call(rbind, r)
#   element          mat
# 1       1           NA
# 2       2 NA, NA, ....