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

next i try...

055  <- tapply(data055$AVERAGE_SACCADE_AMPLITUDE,

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

still nothing....

help? thanks!



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