Pad arrays
Generalized padding for arrays of arbitrary dimension
apad(a, l, e = NULL, method = "ext", post = TRUE)
a |
Array to be padded |
l |
Amount of padding to add. If a vector of length greater than
one, it is interpreted as
the extra extent of |
e |
If |
method |
String specifying the values of the padded elements. See details section. |
post |
Boolean, with default |
Argument method specifies the values of the padded elements.
It can be either “ext”,
“mirror”, or “rep”.
Specifying ext (the default) uses a padding value given by
the “nearest” element of a, as measured by the
Manhattan metric.
Specifying mirror fills the array with alternate mirror
images of a; while rep fills it with unreflected copies
of a.
Function apad() does not work with arrays with dimensions of
zero extent: what to pad it with? To pad with a particular value, use
adiag().
The function works as expected with vectors, which are treated as one-dimensional arrays. See examples section.
Function apad() is distinct from adiag(), which takes
two arrays and binds them together. Both functions create an array of
the same dimensionality as their array arguments but with possibly
larger extents. However, the functions differ in the values of the
new array elements. Function adiag() uses a second array;
function apad() takes the values from its primary array argument.
Robin K. S. Hankin
apad(1:10,4,method="mirror") a <- matrix(1:30,5,6) apad(a,c(4,4)) apad(a,c(4,4),post=FALSE) apad(a,1,5) apad(a,c(5,6),method="mirror") apad(a,c(5,6),method="mirror",post=FALSE)
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