R help - Nov 2008 - How do you apply a function to each variable in a data frame?

I want to apply a more complicated function than what I use in my example,
but the idea is the same:

Suppose you have a data frame named x and you want to a function applied to
each variable, we'll just use the quantile function for this example. 
I'm
trying all sorts of apply functions, but not having luck.  My best guess
would be:

sapply(x, FUN=quantile)
-- 
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Sent from the R help mailing list archive at Nabble.com.

Dear zerftezen,
Try this:

# Data
set.seed(123)
X=as.data.frame(matrix(rnorm(100),ncol=10))

# Percentiles 10 and 90 using apply
t(apply(X,2,quantile,probs=c(0.1,0.9)))

# The same using sapply
t(sapply(X,function(x) quantile(x,probs=c(0.1,0.9))))


HTH,

Jorge



On Mon, Nov 3, 2008 at 10:03 AM, zerfetzen <zerfetzen@yahoo.com> wrote:
>
> I want to apply a more complicated function than what I use in my example,
> but the idea is the same:
>
> Suppose you have a data frame named x and you want to a function applied to
> each variable, we'll just use the quantile function for this example. 
I'm
> trying all sorts of apply functions, but not having luck.  My best guess
> would be:
>
> sapply(x, FUN=quantile)
> --
> View this message in context:
>
http://www.nabble.com/How-do-you-apply-a-function-to-each-variable-in-a-data-frame--tp20304332p20304332.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> R-help@r-project.org 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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On Mon, Nov 3, 2008 at 9:02 AM, Jorge Ivan Velez
<jorgeivanvelez at gmail.com> wrote:
> Dear zerftezen,
> Try this:
>
> # Data
> set.seed(123)
> X=as.data.frame(matrix(rnorm(100),ncol=10))
>
> # Percentiles 10 and 90 using apply
> t(apply(X,2,quantile,probs=c(0.1,0.9)))
>
> # The same using sapply
> t(sapply(X,function(x) quantile(x,probs=c(0.1,0.9))))
An alternative is the colwise function in the plyr package:

library(plyr)
colwise(quantile)(X, probs = c(0.1,0.9))
colwise(quantile)(mtcars,  probs = c(0.1,0.9))

It always returns a data frame.  You can also use catcolwise and
numcolwise which only operate on categorical and numeric columns
respectively.

Hadley

-- 
http://had.co.nz/

Data frames are lists themselves.

Something like

do.call( rbind, lapply( my.data.frame, quantile, probs=c(0.1,0.9)) )

should work.

Carlos J. Gil Bellosta
http://www.datanalytics.com


On Mon, 2008-11-03 at 07:03 -0800, zerfetzen wrote:
> I want to apply a more complicated function than what I use in my example,
> but the idea is the same:
> 
> Suppose you have a data frame named x and you want to a function applied to
> each variable, we'll just use the quantile function for this example. 
I'm
> trying all sorts of apply functions, but not having luck.  My best guess
> would be:
> 
> sapply(x, FUN=quantile)

zerfetzen wrote:
> I want to apply a more complicated function than what I use in my example,
> but the idea is the same:
> 
> Suppose you have a data frame named x and you want to a function applied to
> each variable, we'll just use the quantile function for this example. 
I'm
> trying all sorts of apply functions, but not having luck.  My best guess
> would be:
> 
> sapply(x, FUN=quantile)

And how does that not work?  For me, it does:

test <- data.frame(a = rnorm(100), b = rnorm(100), c = rnorm(100))
sapply(test, quantile)


You should say what you tried and most importantly, *how* you are not 
having luck, i.e., what errors or unexpected results you are getting.

Using small examples like the 'test' data.frame can also help clear up 
misunderstandings.