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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