R help - Jun 2010 - tapply help

Dear R gurus,

I am trying perform what I believe will be a pretty simple task, but I'm
struggling to figure out how to do it. I have two vectors of the same length,
the first is numeric and the second is factor. I understand that tapply is
perfect for applying a function to the numeric vector by subsets of the factors
in the second vector. My issue is trying to make use of two other vectors within
the custom function I've written for tapply. The two other vectors are a
high and low value for each subset I am breaking my data into, and I want to
calculate the percentage of data points that fall into each respective range. I
will attempt to provide a coherent example:

# create range for each possible class
lows<-c(1,2,3,4,5)
highs<-c(5,6,7,8,9)

# data values
vals<-sample(1:10,100,replace=T)

#classes
classes<-sample(letters[1:5],100,replace=T)

# Try to calculate percentage of values that fall
# into the respective range for the given class.
percentages<-tapply(vals,classes,
	function(i){
		length(i[i>=lows[index] & i<=highs[index]])/length(i)  # I don't
know how to actually keep an index count in tapply, but I'm guessing
there's a better way.
	})

I really appreciate any help.

ME

It this what you are looking for:
> set.seed(1)
> # create range for each possible class
> # 'name' the values so you can use them in the 'sapply'
function
> lows<-c(a=1, b=2, c=3, d=4, e=5)
> highs<-c(a=5, b=6, c=7, d=8, e=9)
>
> # data values
> vals<-sample(1:10,100,replace=T)
>
> #classes
> classes<-sample(letters[1:5],100,replace=T)
>
> # split the data so that you retain the 'classes' name
> x.split <- split(vals, classes)
> percentage <- sapply(names(x.split), function(.class){
+     # compute the percentage based on 'class'
+     sum((x.split[[.class]] >= lows[.class]) &
+         (x.split[[.class]] <= highs[.class])) /
length(x.split[[.class]]) * 100
+ })
> percentage
       a        b        c        d        e
50.00000 45.00000 62.50000 54.54545 55.55556
>

On Fri, Jun 4, 2010 at 4:02 PM, Mark Ebbert <Mark.Ebbert at hci.utah.edu>
wrote:
> Dear R gurus,
>
> I am trying perform what I believe will be a pretty simple task, but
I'm struggling to figure out how to do it. I have two vectors of the same
length, the first is numeric and the second is factor. I understand that tapply
is perfect for applying a function to the numeric vector by subsets of the
factors in the second vector. My issue is trying to make use of two other
vectors within the custom function I've written for tapply. The two other
vectors are a high and low value for each subset I am breaking my data into, and
I want to calculate the percentage of data points that fall into each respective
range. I will attempt to provide a coherent example:
>
> # create range for each possible class
> lows<-c(1,2,3,4,5)
> highs<-c(5,6,7,8,9)
>
> # data values
> vals<-sample(1:10,100,replace=T)
>
> #classes
> classes<-sample(letters[1:5],100,replace=T)
>
> # Try to calculate percentage of values that fall
> # into the respective range for the given class.
> percentages<-tapply(vals,classes,
> ? ? ? ?function(i){
> ? ? ? ? ? ? ? ?length(i[i>=lows[index] &
i<=highs[index]])/length(i) ?# I don't know how to actually keep an index
count in tapply, but I'm guessing there's a better way.
> ? ? ? ?})
>
> I really appreciate any help.
>
> ME
> ______________________________________________
> R-help at 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.
>


-- 
Jim Holtman
Cincinnati, OH
+1 513 646 9390

What is the problem that you are trying to solve?