R help - Jul 2007 - summarizing dataframe at variable/factor levels

All,

Is there an efficient way to apply say "mean" or "median" to
a dataframe

according to say all combinations of two variables in the dataframe?
Below is a simple example and the outline of a "manual" solution that
will work but is not very efficient
(could also generalize this to a function).  Searched the archives and
docs but didn't see anything close to this question.

Cheers,
dave

dat.ex = data.frame(  rep(c(1:6), each=6), c(rnorm(12), rnorm(12, 1),
rnorm(12, 2)), rnorm(36, 5), rep(c(1:6), 6),
rep(c("Drug1", "Drug2", "Placebo"), each=12) )
names(dat.ex) = c("patient.no", "outcome", "x",
"time", "drug")

mean of first 2 time pts on Drug1:
mean.time.1.drug.1 = mean( dat.ex[dat.ex$time==1 &
dat.ex$drug=="Drug1",
c(2,3)])
mean.time.2.drug.1 = mean( dat.ex[dat.ex$time==2 &
dat.ex$drug=="Drug1",
c(2,3)])

dat.ex.reduced = as.data.frame(rbind(mean.time.1.drug.1,
mean.time.2.drug.1))
dat.ex.reduced$Drug = c("Drug1", "Drug1")  ## add back Drug
variable and
time variable
dat.ex.reduced$time = c(1,2)

my.data <- data.frame(
	trts <- rep(c('Drug 1','Drug2'), each = 10),
	doses <- rep(c('Low dose','High dose'), 10),
	resp <- rnorm(20)
)


tapply(my.data$resp, list(my.data$trts, my.data$doses), mean)




Jim





Afshartous, David wrote:
> 
> 
> All,
> 
> Is there an efficient way to apply say "mean" or
"median" to a dataframe
> 
> according to say all combinations of two variables in the dataframe?
> Below is a simple example and the outline of a "manual" solution
that
> will work but is not very efficient
> (could also generalize this to a function).  Searched the archives and
> docs but didn't see anything close to this question.
> 
> Cheers,
> dave
> 
> dat.ex = data.frame(  rep(c(1:6), each=6), c(rnorm(12), rnorm(12, 1),
> rnorm(12, 2)), rnorm(36, 5), rep(c(1:6), 6),
> rep(c("Drug1", "Drug2", "Placebo"), each=12)
)
> names(dat.ex) = c("patient.no", "outcome",
"x", "time", "drug")
> 
> mean of first 2 time pts on Drug1:
> mean.time.1.drug.1 = mean( dat.ex[dat.ex$time==1 &
dat.ex$drug=="Drug1",
> c(2,3)])
> mean.time.2.drug.1 = mean( dat.ex[dat.ex$time==2 &
dat.ex$drug=="Drug1",
> c(2,3)])
> 
> dat.ex.reduced = as.data.frame(rbind(mean.time.1.drug.1,
> mean.time.2.drug.1))
> dat.ex.reduced$Drug = c("Drug1", "Drug1")  ## add back
Drug variable and
> time variable
> dat.ex.reduced$time = c(1,2)
> 
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
> http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
> 
> 
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Afshartous, David <afshart <at> exchange.sba.miami.edu> writes:
> All,
> Is there an efficient way to apply say "mean" or
"median" to a dataframe
> according to say all combinations of two variables in the dataframe?
> ..[snip]..
> 
See function summaryBy in package doBy

Try this:

aggregate(dat.ex[2:3], dat.ex[4:5], mean)


On 7/5/07, Afshartous, David <afshart at exchange.sba.miami.edu>
wrote:
>
> All,
>
> Is there an efficient way to apply say "mean" or
"median" to a dataframe
>
> according to say all combinations of two variables in the dataframe?
> Below is a simple example and the outline of a "manual" solution
that
> will work but is not very efficient
> (could also generalize this to a function).  Searched the archives and
> docs but didn't see anything close to this question.
>
> Cheers,
> dave
>
> dat.ex = data.frame(  rep(c(1:6), each=6), c(rnorm(12), rnorm(12, 1),
> rnorm(12, 2)), rnorm(36, 5), rep(c(1:6), 6),
> rep(c("Drug1", "Drug2", "Placebo"), each=12)
)
> names(dat.ex) = c("patient.no", "outcome",
"x", "time", "drug")
>
> mean of first 2 time pts on Drug1:
> mean.time.1.drug.1 = mean( dat.ex[dat.ex$time==1 &
dat.ex$drug=="Drug1",
> c(2,3)])
> mean.time.2.drug.1 = mean( dat.ex[dat.ex$time==2 &
dat.ex$drug=="Drug1",
> c(2,3)])
>
> dat.ex.reduced = as.data.frame(rbind(mean.time.1.drug.1,
> mean.time.2.drug.1))
> dat.ex.reduced$Drug = c("Drug1", "Drug1")  ## add back
Drug variable and
> time variable
> dat.ex.reduced$time = c(1,2)
>
> ______________________________________________
> R-help at stat.math.ethz.ch mailing list
> https://stat.ethz.ch/mailman/listinfo/r-help
> PLEASE do read the posting guide
http://www.R-project.org/posting-guide.html
> and provide commented, minimal, self-contained, reproducible code.
>