Ross Darnell writes:
> I am trying to construct a contingency table of factor levels defined
> as (say 3) columns of a dataframe, X.
>
> table(X) gives a one dimensional table.
>
> apply(X,2,table) gives 3 marginal tables.
>
> table(X$V1,X$V2,X$V3) gives the correct answer but isn't a useful
> method for a general dataframe.
>
> There is obviously a simple solution, but not so obvious to me.
Indeed there are at least two simple solutions.
Suppose `datfr' is a data frame with an arbitrary number, n, of
factor components and I need to find the n-way contingency table
they define. Refugees from SPSS will rejoice in the solution
tab <- crosstabs(~ . , datfr)
but the result carries a lot of extra baggage. If you want just
the bare table with dimnames you will probably want to do:
tab <- structure(crosstabs(~ . , datfr),
marginals = NULL, call = NULL, class = NULL)
The general problem, though, is "How do I call a function with an
arbitrary number of arguments?" and for this there is a general
solution. The following will do it:
tab <- do.call("table", datfr)
It is often a defining moment in many S programmers' lives when
they finally see the need for do.table.
Bill Venables.
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