[R] invalid type error

[Joshua Wiley]

Jason,

Erik already offered a nice solution, but I wanted to comment on why
it did not work.  apply() works on arrays and, of course, matrices.
When you pass a data frame to apply, it will try to coerce it to a
matrix.  Matrices only contain a single class of data (unlike data
frames which can have separate classes for each column).  The
hierarchy is logical < integer < real < complex < character.  Since
a10 is character, everything is converted up to character.  This
causes sum() to fail because it is passed character data.  This also
explain why doit() works if you pass the data frame rows to it
directly  doit(myDF[1 ,]) .

You can find all this in the documentation for ?apply and ?as.matrix

Cheers,

Josh

On Mon, Jul 19, 2010 at 12:36 PM, jd6688 <jdsignature at gmail.com> wrote:
>
>>myDF =
> data.frame(id=c("A10","A20"),d1=c(.3,.3),d2=c(.4,.4),d3=c(-.2,.5),d4=c(-.3,.6),d5=c(.5,-.2),d6=c(.6,-.4),d7=c(-.9,-.5),d8=c(-.8,-.6))
>
>>doit=function(x)c(x[1],sum_LK_positive=sum(x[-1][x[-1]>0]),sum_LK_negative=sum(x[-1][x[-1]<0]))
>
>> myDF
>   id  d1  d2   d3   d4   d5   d6   d7   d8
> 1 A10 0.3 0.4 -0.2 -0.3  0.5  0.6 -0.9 -0.8
> 2 A20 0.3 0.4  0.5  0.6 -0.2 -0.4 -0.5 -0.6
>>  t(apply(myDF,1,doit))
>
>
> Error in sum(x[-1][x[-1] > 0]) : invalid 'type' (character) of argument:
>
> I changed the id=c(100,101) in myDF, it worked. are there any way to have
> this working if the id=c("a10","a20")?
>
> Thanks,
>
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-- 
Joshua Wiley
Ph.D. Student, Health Psychology
University of California, Los Angeles
http://www.joshuawiley.com/