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

get.var {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

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)

[Package mgcv version 1.4-1.1 Index]