Transforming a string into a command
Hi
Did my reply get orphaned or are you trying to help me realize that
asking
why something does not work is not a straightforward question? I'll try
to
cover both bases. I'll focus just on the first case that I don't understand. Suppose we
have
s<- "ln(a+b)" a<-1 b<-2 eval(parse(text=s)) Error in eval(expr, envir, enclos) : could not find function "ln"
What is function ln supposed to do and to what package it belongs. I get
?ln
No documentation for ?ln? in specified packages and libraries: you could try ???ln? but it does not mean that ln is not used elsewhere. Regards Petr
Perhaps it's because I don't understand eval well (any good references
for
reading up on eval, parse, substitute, etc.?). But I expected it to
produce
the same as the following line: eval(parse(text="ln(a+b)")) Xu David Winsemius wrote
On Nov 29, 2011, at 2:00 AM, Xu Wang wrote:
Why don't the following two commands work? eval(parse(text=s)) eval(as.expression(s))
Can you think of anything else we might need to know in order to answer that question? -- David Winsemius, MD West Hartford, CT
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