[R] tapply output

[Erik Iverson]

Hello,

You can use ddply from the very useful plyr package to do this.
There must be a way using "base R" functions, but plyr is
worth looking into in my opinion.

 > install.packages("plyr")
 > library(plyr)
 > ddply(myData, .(class, group, name), function(x) mean(x$height))

   class group name   V1
1     0     A  Tom 62.5
2     0     B Jane 58.5
3     1     A Enzo 66.5
4     1     B Mary 70.5

Geoffrey Smith wrote:
> Hello, I am having trouble getting the output from the tapply function
> formatted so that it can be made into a nice table.  Below is my question
> written in R code.  Does anyone have any suggestions?  Thank you.  Geoff
> 
> #Input the data;
> name <- c('Tom', 'Tom', 'Jane', 'Jane', 'Enzo', 'Enzo', 'Mary', 'Mary');
> year <- c(2008, 2009, 2008, 2009, 2008, 2009, 2008, 2009);
> group <- c('A', 'A', 'B', 'B', 'A', 'A', 'B', 'B');
> class <- c(0, 0, 0, 0, 1, 1, 1, 1);
> height <- c(62, 63, 59, 58, 67, 66, 70, 71);
> 
> #Combine the data into a data frame;
> myData <- data.frame(name, year, group, class, height);
> myData;
> 
> #Calculate the mean of height by class, group, and name;
> tapply(myData$height, data.frame(myData$class, myData$group, myData$name),
> mean);
> 
> #The raw output from the tapply function is fine, but I would;
> #really like the output to look like this;
> #  class   group     name     mean
> #    0       A            Tom        62.5
> #    0       B            Jane        58.5
> #    1       A            Enzo       66.5
> #    1       B            Mary       70.5
>