apply with missing values

I am trying to get the means of each participants avg saccade  
amplitude as a
function of the group they were in (designated by "shape_"), but  
there are
missing values in the dataset....this is what i tried...

with(data055,tapply(AVERAGE_SACCADE_AMPLITUDE,shape_,mean))
i get an error saying the argument is not numerical or logical

The error message appears informative (and would NOT be expected to be  
solved by adding na.rm=TRUE). Your construction of the data055  
dataframe was flawed in some way. You have not shown how it was done  
nor given dput(head(data055)) which would have provided a basis for  
further assessment. Based on past experience my guess is that there  
was a character value in the column of data you thought was numeric  
during a read.* operation and is now a factor.

next i try...

055  <- tapply(data055$AVERAGE_SACCADE_AMPLITUDE,

+ data055$shape_,mean, na.rm =TRUE)

still nothing....

David Winsemius, MD
Alameda, CA, USA