Returns a list with the concatenated feature matrices in slot x (\((\sum_i^q n_i) \times p\) matrix), the concatenated target vectors in slot y (vector of length \((\sum_i^q n_i)\)), and the indices of the problems in slot index (vector of length \((\sum_i^q n_i)\) with entries \(1,\ldots,q\)).
Arguments
x
list of \(q\) matrices, with \(n_1,\ldots,n_q\) rows
and with \(p\) columns
y
list of \(q\) vectors, of length \(n_1,\ldots,n_q\),
or NULL (default)
foldid
list of \(q\) vectors, of length \(n_1,\ldots,n_q\),
or NULL (default)