[R] Warning: condition has length > 1

[Roger Bivand]

On Sat, 8 Oct 2005, nawaf b wrote:

> Hi -
> 
> I was wondering if anyone came across a problem such as mine! I was trying
> to create a user-defined function, however, the results from calling the
> function are unexpected!
> 
> When passing X parameter as a single value variable (x<-c(3)), everything
> works fine. However, when passing a parameter as a vector with multiple
> values (as the case in my code), the 'if condition' is only executed once!
> 
> Here is my code:
> > x
> [1]  0.3  1.0  0.7 22.0
> > myfunction<-function(x)
> + {
> + if (x>=1) 0
> + else x^2
> + }
> > myfunction(x)
> [1]   0.09   1.00   0.49 484.00
> Warning message:
> the condition has length > 1 and only the first element will be used in: if
> (x >= 1) 0 else x^2 
> >
> 
> Is there a way to overcome this issue? Can you please explain what
> modifications to the code I need to accommodate to make it work.

> myfunction<-function(x)
+ ifelse(x>=1, 0, x^2)
> x <- c(0.3, 1.0, 0.7, 22.0)
> myfunction(x)
[1] 0.09 0.00 0.49 0.00

ifelse() is vectorised, but if() only looks at the first element in x 
before deciding what to do - so if the condition is longer, the rest gets 
ignored.

> 
> Thanks,
> 
> Nawaf
> 
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-- 
Roger Bivand
Economic Geography Section, Department of Economics, Norwegian School of
Economics and Business Administration, Helleveien 30, N-5045 Bergen,
Norway. voice: +47 55 95 93 55; fax +47 55 95 95 43
e-mail: Roger.Bivand at nhh.no