[R] eval(expr) without printing to screen?

[Nick Matzke]

Hi,

I have a script which I source, which evaluates a changing expression 
call hundreds of times.  It works, but it prints to screen each time, 
which is annoying.  There must be simple way to suppress this, or to use 
a slightly different set of commands, which will be obvious to those 
wiser than I...


Here is a simpler mockup which shows the issue:

x = data.frame(rbind(c(1,2,3),c(1,2,3)))
xnames = c("a", "b", "c")
names(x) = xnames

for(i in 1:length(x))
{
# Create a varying string expression
expr = paste("y = x$", xnames[i], "[1]", sep="")

# evaluate expression
eval(parse(text=print(expr)))

# This command prints the expression to screen even when embedded in a 
function in a sourced script.  I would prefer it didn't!
}


PS: I have to go through this rigamarole:

expr = "y1 = x$c[1]"
eval(parse(text=print(expr)))

Because the following doesn't work, even though it seems like it should:
expr = "y = x$c[2]"
eval(expr)




-- 
====================================================
Nicholas J. Matzke
Ph.D. Candidate, Graduate Student Researcher
Huelsenbeck Lab
Center for Theoretical Evolutionary Genomics
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University of California, Berkeley

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