| slice.index {base} | R Documentation |
Slice Indexes in an Array
Description
Returns a matrix of integers indicating the number of their slice in a given array.
Usage
slice.index(x, MARGIN)
Arguments
x |
an array. If |
MARGIN |
an integer vector giving the dimension numbers to slice by. |
Details
If MARGIN gives a single dimension, then all elements of slice
number i with respect to this have value i. In general,
slice numbers are obtained by numbering all combinations of indices in
the dimensions given by MARGIN in column-major order. I.e.,
with m_1, ..., m_k the dimension numbers (elements of
MARGIN) sliced by and d_{m_1}, ..., d_{m_k} the
corresponding extents, and n_1 = 1, n_2 = d_{m_1}, ...,
n_k = d_{m_1} \cdots d_{m_{k-1}},
the number of the slice where dimension m_1 has value i_1,
..., dimension m_k has value i_k is
1 + n_1 (i_1 - 1) + \cdots + n_k (i_k - 1).
Value
An integer array y with dimensions corresponding to those of
x.
See Also
row and col for determining row and column
indexes; in fact, these are special cases of slice.index
corresponding to MARGIN equal to 1 and 2, respectively when
x is a matrix.
Examples
x <- array(1 : 24, c(2, 3, 4))
slice.index(x, 2)
slice.index(x, c(1, 3))
## When slicing by dimensions 1 and 3, slice index 5 is obtained for
## dimension 1 has value 1 and dimension 3 has value 3 (see above):
which(slice.index(x, c(1, 3)) == 5, arr.ind = TRUE)