Hello,
Reeyarn_李智洋_10928113 wrote
>
> Hi, I want to run something like
> SELECT firm_id, count(*), mean(value), sd(value)
> FROM table
> GROUP BY firm_id;
>
> But I have to write a for loop like
> for ( id in unique(table$firm_id ) {
> print(paste( id, mean(table[firm_id == id, "value"]) ))
> }
>
> Is there any way to do it easier? Thanks :)
>
>
> Best,
> Reeyarn Lee
>
> [[alternative HTML version deleted]]
>
> ______________________________________________
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> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>
You can use sql with package 'sqldf'.
library(sqldf) # It needs package 'tcltk'
?sqldf
tbl <- data.frame(firm_id=rep(c(1,2), 10), value=rnorm(20))
sqldf("SELECT firm_id, count(*), avg(value), stdev(value)
FROM tbl
GROUP BY firm_id;")
I've changed the name of your data.frame because 'table' is an R function.
Hope this helps,
Rui Barradas
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