The one most often used function in the analysis of statistical data is the creation of tables. This edition of the R-Sessions describes the use of several functions to do some nifty cross-tabulations. And more.

## TAPPLY

The function TAPPLY can be used to perform calculations on table-marginals. Different functions can be used, such as MEAN, SUM, VAR, SD, LENGTH (for frequency-tables). For example:

x <- c(0,1,2,3,4,5,6,7,8,9)

y <- c(1,1,1,1,1,1,2,2,2,2)

tapply(x,y,mean)

tapply(x,y,sum)

tapply(x,y,var)

tapply(x,y,length)

> x <- c(0,1,2,3,4,5,6,7,8,9) > y <- c(1,1,1,1,1,1,2,2,2,2) > tapply(x,y,mean) 1 2 2.5 7.5 > tapply(x,y,sum) 1 2 15 30 > tapply(x,y,var) 1 2 3.500000 1.666667 > tapply(x,y,length) 1 2 6 4 >

## FTABLE

More elaborate frequency tables can be created with the FTABLE-function. For example:

x <- c(0,1,2,3,4,5,6,7,8,9)

y <- c(1,1,1,1,1,1,2,2,2,2)

z <- c(1,1,1,2,2,2,2,2,1,1)

ftable(x,y,z)

> x <- c(0,1,2,3,4,5,6,7,8,9) > y <- c(1,1,1,1,1,1,2,2,2,2) > z <- c(1,1,1,2,2,2,2,2,1,1) > ftable(x,y,z) z 1 2 x y 0 1 1 0 2 0 0 1 1 1 0 2 0 0 2 1 1 0 2 0 0 3 1 0 1 2 0 0 4 1 0 1 2 0 0 5 1 0 1 2 0 0 6 1 0 0 2 0 1 7 1 0 0 2 0 1 8 1 0 0 2 1 0 9 1 0 0 2 1 0

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R-Sessions is a collection of manual chapters for R-Project, which are maintained on Curving Normality. All posts are linked to the chapters from the R-Project manual on this site. The manual is free to use, for it is paid by the advertisements, but please refer to it in your work inspired by it. Feedback and topic requests are highly appreciated.
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