Contrast matrices
Return a matrix of contrasts for factor coding.
contr.cum(n) contr.diff(n) contr.2nd(n) contr.orth(n)
n |
A vector of levels for a factor, or the number of levels. |
These functions are used for creating contrast matrices for use in
fitting regression models. The columns of the
resulting matrices contain contrasts which can be used for coding a
factor with n levels.
contr.cum gives a coding corresponding to successive differences
between factor levels.
contr.diff gives a coding that correspond to the cumulative sum
of the value for each level. This is not meaningful in a model where the
intercept is included, therefore n columns ia always returned.
contr.2nd gives contrasts corresponding to 2nd order differences
between factor levels. Returns a matrix with n-2 columns.
contr.orth gives a matrix with n-2 columns, which are
mutually orthogonal and orthogonal to the matrix cbind(1,1:n)
A matrix with n rows and k columns, with
k=n for contr.diff
k=n-1 for contr.cum
k=n-2 for contr.2nd and contr.orth.
Bendix Carstensen
contr.cum(6) contr.2nd(6) contr.diff(6) contr.orth(6)
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