[R] Transforming a string into a command
Xu Wang
xuwang762 at gmail.com
Tue Nov 29 08:30:47 CET 2011
David,
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"
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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