Loops are time consuming in R. Try one of the apply functions for vectorized 
calculations, like "apply", "lapply","sapply" or "tapply". Also see help for 
"split".

In a message dated 10/19/03 5:25:51 PM Pacific Daylight Time, 
Wanzare@HCJP.com writes:

> Hello All,
>       I am new to R. I am trying to process this huge data set of
> matrix containing four columns, say x1, x2, x3, x4 and n number of rows.
> 
> I want to aggregate the matrix by x1 and perform statistic based on
> columns x2, x3, x4. I tried aggregate function but it gave me memory
> allocation error (which I am not surprised), so I ended up performing a
> for loop based on x1 and subsetting the matrix based on x1. However I
> have a hunch that their should be a less expensive way of doing this
> processing.  Any ideas or tips to optimize this processing logic would
> be greatly appreciated.
> 


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