a vector giving the subscripts to split up data by.
.expand
if splitting a dataframe by row, should output be 1d
(expand = FALSE), with an element for each row; or nd (expand = TRUE),
with a dimension for each variable.
.id
names of the split label.
Pass NULL to avoid creation of split labels.
Omit or pass NA to use the default names
"X1", "X2", ....
Otherwise, this argument must have the same length as
.margins.
Details
This is the workhorse of the a*ply functions. Given a >1 d
data structure (matrix, array, data.frame), it splits it into pieces
based on the subscripts that you supply. Each piece is a lower dimensional
slice.
The margins are specified in the same way as apply, but
splitter_a just splits up the data, while apply also
applies a function and combines the pieces back together. This function
also includes enough information to recreate the split from attributes on
the list of pieces.
Value
a list of lower-d slices, with attributes that record split details