R help - Jun 2010 - Calculating Summaries for each level of a Categorical variable

Hi,

I have a dataset which has a categorical variable "R",a count variable
C
(integer) and 4 or more numeric variables (A,T,W,H - integers) containing
measures for "R". I would like to summarize each level of the variable
R by
the average for A,T,W and H. 

I have written a function to calculate weighted averages using C as the
weight and this is given below. The function works perfectly but how do I
add the additional dimension I require to this function?

Dataset: RTR     A  T   W   H
R1   10 20 20  10
R2   60 20 50  10
R3   45 10 20  50
R4   68 50 20  10
R1   73 20 40  46
R3   25 30 10  54
R3   36 90 20  10
R2   29 10 30  30

# FUNCTION TO CALCULATE THE WEIGHTED AVERAGE FOR A WEIGHTED BY C
WA<-function(A,C) {
         sp_A<-c(A %*% C)
         sum_C<-sum(C)
         WA<-sp_A/sum_C   
         return(WA)      
         }

I am trying to incorporate the additional step of calculating the weighted
average of A,T,W and H for each level of R. Need help with this.

Thanks in advance!
Raoul
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Did you try tapply?
?tapply

tapply(RT, RT$R, fun=WA)

or something like that

-----
Corey Sparks, PhD
Assistant Professor
Department of Demography and Organization Studies
University of Texas at San Antonio
501 West Durango Blvd
Monterey Building 2.270C
San Antonio, TX 78207
210-458-3166
corey.sparks 'at' utsa.edu
https://rowdyspace.utsa.edu/users/ozd504/www/index.htm
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Look at the summary.formula function inside package Hmisc

Christos
> Date: Sat, 26 Jun 2010 05:17:34 -0700
> From: raoul.t.dsouza@gmail.com
> To: r-help@r-project.org
> Subject: [R] Calculating Summaries for each level of a Categorical variable
> 
> 
> Hi,
> 
> I have a dataset which has a categorical variable "R",a count
variable C
> (integer) and 4 or more numeric variables (A,T,W,H - integers) containing
> measures for "R". I would like to summarize each level of the
variable R by
> the average for A,T,W and H. 
> 
> I have written a function to calculate weighted averages using C as the
> weight and this is given below. The function works perfectly but how do I
> add the additional dimension I require to this function?
> 
> Dataset: RT> R     A  T   W   H
> R1   10 20 20  10
> R2   60 20 50  10
> R3   45 10 20  50
> R4   68 50 20  10
> R1   73 20 40  46
> R3   25 30 10  54
> R3   36 90 20  10
> R2   29 10 30  30
> 
> # FUNCTION TO CALCULATE THE WEIGHTED AVERAGE FOR A WEIGHTED BY C
> WA<-function(A,C) {
>          sp_A<-c(A %*% C)
>          sum_C<-sum(C)
>          WA<-sp_A/sum_C   
>          return(WA)      
>          }
> 
> I am trying to incorporate the additional step of calculating the weighted
> average of A,T,W and H for each level of R. Need help with this.
> 
> Thanks in advance!
> Raoul
> -- 
> View this message in context:
http://r.789695.n4.nabble.com/Calculating-Summaries-for-each-level-of-a-Categorical-variable-tp2269349p2269349.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.
 		 	   		  
_________________________________________________________________
Hotmail: Powerful Free email with security by Microsoft.

	[[alternative HTML version deleted]]

Hi Corey,

Thanks so much for this. However, I get this error for tapply - "Error in
tapply(RT, RT$R, fun=WA): 
  arguments must have same length". Any idea how to get around this?

Thanks again,
Raoul
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Hi Christos,

Thanks for this. I had a look at Summary.Forumla in the Hmisc package and it
is extremely complicated for me. Still trying to decipher how I could use
it.

Regards,
Raoul
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View this message in context:
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You could try the remix function in remix package.

David

Le 27 juin 2010 ? 06:48, RaoulD <raoul.t.dsouza at gmail.com> a ?crit :
>
> Hi Christos,
>
> Thanks for this. I had a look at Summary.Forumla in the Hmisc
> package and it
> is extremely complicated for me. Still trying to decipher how I
> could use
> it.
>
> Regards,
> Raoul
> --
> View this message in context:
http://r.789695.n4.nabble.com/Calculating-Summaries-for-each-level-of-a-Categorical-variable-tp2269349p2269816.html
> Sent from the R help mailing list archive at Nabble.com.
>
> ______________________________________________
> 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.

Hi Raoul, 
I presume you need these summaries for a table of descriptive statistics for a
thesis/report/paper
("Table 1" as known informally by medical researchers). If this is the
case, then specify
method="reverse" to summary.formula. In the following small example, I
create 4 groups of patients
and specify 2 characteristics per patient (age and gender) and use
summary.formula to summarize
characteristics by group. Running the stats on patient characteristics by group
is optional but
is included for completeness. If you are looking for something like this I
strongly advise you spent
some time fiddling around with summary.formula and read: 

Harrell FE (2004): Statistical tables and plots using S and LaTeX 
(available from
http://biostat.mc.vanderbilt.edu/twiki/pub/Main/StatReport/summary.pdf

The 2-3 hours you are going to need to familiarize yourself with this package
are really worth spending
for (especially if you are going to use call LaTEX on the output). If you are a
Windows user, copy and
paste the output of the print function into Excel or OpenOffice and use the Text
to Columns facilities
of the two programs to format the output into a table that can be used inside a
manuscript.

Christos

## R-code follows

library(Hmisc)
## One baseline factor (e.g. patient group)
grp<-round(runif(20,1,4))
grp<-factor(grp,labels=paste("Group",1:4))

## Another factor (e.g. sex)
sex<-round(runif(20,1,2))
sex<-factor(sex,labels=c("Male","Female"))

## A continuous variable (e.g. age)
age<-rlnorm(20,4,.1)

## A data frame
data<-data.frame(age=age,grp=grp,sex=sex)

## Table 1
sm<-summary(grp~sex+age,method="reverse",overall=T,test=T)
print(sm,dig=2,exclude1=F)

Descriptive Statistics by grp

+----------+------------------+------------------+------------------+------------------+------------------+----------------------------+
|????????? |Group 1?????????? |Group 2?????????? |Group 3?????????? |Group
4?????????? |Combined????????? |? Test????????????????????? |
|????????? |(N=3)???????????? |(N=6)???????????? |(N=8)????????????
|(N=3)???????????? |(N=20)??????????? |Statistic?????????????????? |
+----------+------------------+------------------+------------------+------------------+------------------+----------------------------+
|sex : Male|????????? 67% ( 2)|????????? 67% ( 4)|????????? 25% ( 2)|?????????
67% ( 2)|????????? 50% (10)|Chi-square=3.3 d.f.=3 P=0.34|
+----------+------------------+------------------+------------------+------------------+------------------+----------------------------+
|??? Female|????????? 33% ( 1)|????????? 33% ( 2)|????????? 75% ( 6)|?????????
33% ( 1)|????????? 50% (10)|??????????????????????????? |
+----------+------------------+------------------+------------------+------------------+------------------+----------------------------+
|age?????? |????????? 60/62/65|????????? 51/55/60|????????? 46/51/57|?????????
46/48/52|????????? 49/54/60|?? F=2.9 d.f.=3,16 P=0.068? |
+----------+------------------+------------------+------------------+------------------+------------------+----------------------------+

? 
> Date: Sat, 26 Jun 2010 21:48:05 -0700
> From: raoul.t.dsouza at gmail.com
> To: r-help at r-project.org
> Subject: Re: [R] Calculating Summaries for each level of a Categorical
variable
> 
> 
> Hi Christos,
> 
> Thanks for this. I had a look at Summary.Forumla in the Hmisc package and
it
> is extremely complicated for me. Still trying to decipher how I could use
> it.
> 
> Regards,
> Raoul
> -- 
> View this message in context:
http://r.789695.n4.nabble.com/Calculating-Summaries-for-each-level-of-a-Categorical-variable-tp2269349p2269816.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> 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.
 		 	   		  
_________________________________________________________________
Hotmail: Free, trusted and rich email service.

The problem is that tapply is expecting a vector for the first argument, your
first argument is a list or data frame, so the length that it sees is the number
of list elements (columns of the data frame).  You need to either pass a single
vector, or use functions like aggregate or the plyr package to work on all the
columns in a data frame.

-- 
Gregory (Greg) L. Snow Ph.D.
Statistical Data Center
Intermountain Healthcare
greg.snow at imail.org
801.408.8111

> -----Original Message-----
> From: r-help-bounces at r-project.org [mailto:r-help-bounces at r-
> project.org] On Behalf Of RaoulD
> Sent: Saturday, June 26, 2010 10:47 PM
> To: r-help at r-project.org
> Subject: Re: [R] Calculating Summaries for each level of a Categorical
> variable
> 
> 
> Hi Corey,
> 
> Thanks so much for this. However, I get this error for tapply - "Error
> in
> tapply(RT, RT$R, fun=WA):
>   arguments must have same length". Any idea how to get around this?
> 
> Thanks again,
> Raoul
> --
> View this message in context:
> http://r.789695.n4.nabble.com/Calculating-Summaries-for-each-level-of-
> a-Categorical-variable-tp2269349p2269815.html
> Sent from the R help mailing list archive at Nabble.com.
> 
> ______________________________________________
> 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.