"xifti" or pair of "xifti"s.Apply a univariate transformation to each value in a "xifti" or pair of
"xifti"s. If a pair, they must share the same dimensions (brainstructures)
and number of measurements.
transform_xifti(xifti, FUN, xifti2 = NULL, idx = NULL, ...)The xifti
The function. If xifti2 is not provided, it should be
a univariate function like log or sqrt. If
xifti2 is provided, it should take in two arguments, like `+`
or pmax.
The second xifti, if applicable. Otherwise, NULL (default)
The column indices for which to apply the transformation.
If NULL (default), apply to all columns. If two "xifti" objects,
were provided, the values in the first (xifti) will be retained for columns
that are not transformed.
Additional arguments to FUN
A "xifti" storing the result of applying FUN to the input(s).
The data dimensions will be the same. The metadata of xifti will be retained,
and the metadata of xifti2 will be discarded (if provided).
If the "xifti" had the dlabel intent, and the transformation creates
any value that is not a label value (e.g. a non-integer), then it is converted
to a dscalar.
Technically, the function does not have to be univariate: it only has to return the
same number of values as the input. The function will be applied to the matrix
for each brain structure separately. For example, the function
function(q){(q - mean(q)) / sd(q)} will scale each brainstructure, while
scale will scale each column of each brainstructure.
Other functions for manipulating `xifti` objects:
add_surf(),
apply_xifti(),
combine_xifti(),
convert_to_dlabel(),
merge_xifti(),
newdata_xifti(),
remove_xifti(),
select_xifti()