

   NNuummbbeerr ooff RReepplliiccaattiioonnss ooff TTeerrmmss

        replications(formula, data=NULL, na.action=na.fail)

   AArrgguummeennttss::

    formula: a formula or a terms object or a data frame

       data: a data frame used  to  find  the  objects in `for-
             mula'

   na.action: function for handling missing values

   DDeessccrriippttiioonn::

        Returns a vector or a list of the number of replicates
        for each term in the formula.

   DDeettaaiillss::

        If `formula' is a data frame and `data' is missing,
        `formula' is used for `data' with the formula `~ .'.

   VVaalluuee::

        A vector or list with one entry for each term in the
        formula giving the number(s) of replications for each
        level. If all levels are balanced (have the same number
        of replications) the result is a vector, otherwise it
        is a list with a component for each terms, as a vector,
        matrix or array as required.

        A test for balance is `!is.list(replications(for-
        mula,data))'.

   AAuutthhoorr((ss))::

        B.D. Ripley

   SSeeee AAllssoo::

        `model.tables'

   EExxaammpplleess::

        ## From Venables and Ripley (1997) p.210.
        N <- c(0,1,0,1,1,1,0,0,0,1,1,0,1,1,0,0,1,0,1,0,1,1,0,0)
        P <- c(1,1,0,0,0,1,0,1,1,1,0,0,0,1,0,1,1,0,0,1,0,1,1,0)
        K <- c(1,0,0,1,0,1,1,0,0,1,0,1,0,1,1,0,0,0,1,1,1,0,1,0)
        yield <- c(49.5,62.8,46.8,57.0,59.8,58.5,55.5,56.0,62.8,55.8,69.5,
        55.0, 62.0,48.8,45.5,44.2,52.0,51.5,49.8,48.8,57.2,59.0,53.2,56.0)

        npk <- data.frame(block=gl(6,4), N=factor(N), P=factor(P),
                          K=factor(K), yield=yield)
        replications(~. - yield, npk)

