[R] substitute, eval, quote and functions

David A. van Leeuwen myfirstname at elseware.nl
Mon Feb 9 00:07:55 CET 2004


i am working with large data frames with many dependend variables.  I 
want to write some functions that will allow me to quickly select 
variables from the frame and plot them in various colors depending on 
factor columns, possibly selecting rows according to factor conditions. 

In order to do this in a nice function, i need to understand how to work 
with a column name in the body of a function. 

To simplify my problem, how do i write a function with a body like

scatter.plot <- function (data, x, y) {
    plot(data$x, data$y)

(which doesn't work, of course---i need a series of `substitute's and 
evals---but i can't get it to work---in Perl it would be something along 
the lines of $$x, dereferencing $x another time)
so that i can call

scatter.plot(x, one, two)

as a `short' for

plot(x$one, x$two)

In my real application I want to pass the `column selecting' arguments 
to `subset', which evan with the code of subset.data.frame I have not 
been successful after a whole evening...


David A. van Leeuwen			< @ElseWare.nl>

	  Echt stijlvol sterven doe je / bij een ander op de mat
	  Op de dag dat je bezorgd wordt / door het NRC Handelsblad
							---Joop Visser

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