[R] working with summarized data

Rick Bischoff rdbisch at gmail.com
Wed Aug 30 16:27:58 CEST 2006

The data sets I am working with all have a weight variable--e.g.,  
each row doesn't mean 1 observation.

With that in mind, nearly all of the graphs and summary statistics  
are incorrect for my data, because they don't take into account the  

For example "median" is incorrect, as the quantiles aren't calculated  
with weights:

sum( weights[X < median(X)] ) / sum(weights)

This should be 0.5... of course it's not.

Unfortunately, it seems that most(all?) of R's graphics and summary  
statistic functions don't take a weight or frequency argument.    
(Fortunately the models do...)

Am I completely missing how to do this?  One way would be to  
replicate each row proportional to the weight (e.g. if the weight was  
4, we would 3 additional copies) but this will get prohibitive pretty  
quickly as the dataset grows.

Thanks in advance!

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