get.var                 package:mgcv                 R Documentation

Get named variable or evaluate expression from list or data.frame

Description:

     This routine takes a text string and a data frame or list. It
     first sees if the  string is the name of a variable in the data
     frame/ list. If it is then the value of this variable is returned.
      Otherwise the routine tries to evaluate the expression within the
     data.frame/list (but nowhere else) and if  successful returns the
     result. If neither step works then 'NULL' is returned. The routine
     is useful for processing gam formulae. If the variable is a matrix
     then it is coerced to a numeric vector, by default.

Usage:

      get.var(txt,data,vecMat=TRUE)

Arguments:

     txt: a text string which is either the name of a variable in
          'data' or when  parsed is an expression that can be evaluated
          in 'data'. It can also be neither in which case the function
          returns 'NULL'.

    data: A data frame or list.

  vecMat: Should matrices be coerced to numeric vectors?

Value:

     The evaluated variable or 'NULL'. May be coerced to a numeric
     vector if it's a matrix.

Author(s):

     Simon N. Wood simon.wood@r-project.org

References:

     <URL: http://www.maths.bath.ac.uk/~sw283/>

See Also:

     'gam '

Examples:

     y <- 1:4;dat<-data.frame(x=5:10)
     get.var("x",dat)
     get.var("y",dat)
     get.var("x==6",dat)
     dat <- list(X=matrix(1:6,3,2))
     get.var("X",dat)

