[R] Comparison of aggregate in R and group by in mysql

[Gabor Grothendieck]

How does the it compare if you read it into R and then do your
aggregate with sqldf:

library(sqldf)

# example using builtin data set CO2
CO2agg <- sqldf("select Plant, Type, Treatment, avg(conc) from CO2
group by Plant, Type, Treatment")

# or using your data:

Xagg <- sqldf("select Group, Age, Type, avg(Salary) from X group by
Group, Age, Type")


On Jan 26, 2008 6:45 PM, zhihuali <lzhtom at hotmail.com> wrote:
>
> Hi, netters,
>
> First of all, thanks a lot for all the prompt replies to my earlier question about "merging" data frames in R.
> Actually that's an equivalence to the "join" clause in mysql.
>
> Now I have another question. Suppose I have a data frame X with lots of columns/variables:
> Name, Age,Group, Type, Salary.
> I wanna do a subtotal of salaries:
> aggregate(X$Salary, by=list(X$Group,X$Age,X$Type),Fun=mean)
>
> When the levels of Group and Type are huge, it took R forever to finish the aggregation.
> And I used gc to find that the memory usage was big too.
>
> However, in mysql, it took seconds to finish a similar job:
> select Group,Age,Type ,avg(Salary)  from X group by  Group,Age,Type
>
> Is it because mysql is superior in doing such kind of things? Or my R command is not efficient enough? Why did R have to consume huge memories to do the aggregation?
>
> Thanks again!
>
> Zhihua Li
>
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