[R] SQL like manipulations on data frames

[bogdan romocea]

This goes the other way - all SQL manipulations are a subset of what
can be done with R. Read up on indexing and see ?merge, ?aggregate,
?by, ?tapply, among others. (For the R equivalent to your query, check
?grep and ?order, and search the list if needed.) Also, this example
might be a good start:

gby <- function(var,BY,byname="BY")
{
if (!exists("summarize")) library(Hmisc)    #you need to install Hmisc
grouped <- summarize(var,BY,function(x) {c(count=length(x),min=min(x),
    max=max(x),mean=mean(x))})
colnames(grouped) <- c(byname,"count","min","max","mean")
grouped
}
#---------------
x <- rnorm(1000)
state <- sample(c("A","B","C","D"),1000,replace=TRUE)
city <- sample(1:5,1000,replace=TRUE)
gby(x,paste(state,city,sep="-"),"State-City")


> -----Original Message-----
> From: r-help-bounces at stat.math.ethz.ch
> [mailto:r-help-bounces at stat.math.ethz.ch] On Behalf Of Robert Citek
> Sent: Thursday, May 04, 2006 6:56 PM
> To: r-help at stat.math.ethz.ch
> Subject: [R] SQL like manipulations on data frames
>
>
> Is there a cheat-sheet anywhere that describes how to do SQL-like
> manipulations on a data frame?
>
> My knowledge of R is rather limited.  But from my experience
> it seems
> as though one can think of data frames as being similar to tables in
> a database: there are rows, columns, and values.  Also, one can
> perform similar manipulations on a data frame as one can on a
> table.
> For example:
>
>   select * from foo where bar < 10 ;
>
> is similar to
>
>   foo[foo["bar"] < 10,]
>
> I'm just wondering how many other SQL-like manipulations can be done
> on a data frame?  As an extreme example, is it reasonable to assume
> there is an R equivalent to:
>
> select bar, bat, baz, baz*100 as 'pctbaz' from foo where bar
> like %xyz
> % order by bat, baz desc ;
>
> Regards,
> - Robert
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