[R] Substitution of the *value* of a variable

Daniel Mastropietro mastropi at uwalumni.com
Mon Jul 22 21:57:46 CEST 2002


I have the following situation:

Suppose I have the string "test(x)", and I want to substitute x by y. I 
know that this can be done by using the following commands:

string <- parse( text="test(x)" )[[1]];
do.call("substitute" , list(string, list(x=as.name("y")));

Now, suppose that the variable name that plays the role of argument in 
"test(x)" may change. That is the string could be "test(z)", "test(w)", 
etc. I have the variable name stored in another variable, say 'varname'. 
That is, I have:

varname <- "w";	# the value of varname is defined by the user and may change.
string <- parse( text=paste("test(" , varname ,")") )[[1]];

How can I have the *value* of 'varname' in 'string' be substituted by 'y'?

Daniel Mastropietro

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