[R] If(cond) statement

[Chuck Cleland]

On 4/29/2008 1:21 PM, Beck, Kenneth (STP) wrote:
> Why will this simple statement not work? I think I am following the
> documentation for if(cond) statements, and I have tried wrapping the
> cons.expr and alt.expr in {}, I get the same error. There is no example
> in the help file, and this is not covered in the Introduction to R,
> SimpleR or other tutorials I have looked into.
> 
> mxx=max(cpx_list$nMV);
> mxy=max(trend_list$nMV);
> if (mxx>mxy)
>   mxy=mxx
> else
>   mxx=mxy
> 
> Error: unexpected 'else' in "else"
> 
> Why does this error message have the first 'else' in single quote and
> second in double??

   Did you see this part of the help page?

"Note that it is a common mistake to forget to put braces ({ .. }) 
around your statements, e.g., after if(..) or for(....). In particular, 
you should not have a newline between } and else to avoid a syntax error 
in entering a if ... else construct at the keyboard or via source. For 
that reason, one (somewhat extreme) attitude of defensive programming is 
to always use braces, e.g., for if clauses."

   Try this:

if (mxx > mxy) mxy <- mxx else mxx <- mxy

   Or this:

{if (mxx > mxy)
mxy <- mxx
else
mxx <- mxy}

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> and provide commented, minimal, self-contained, reproducible code. 

-- 
Chuck Cleland, Ph.D.
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