Zuur: Chapter 4: Simple Functions

 

the tapply function

-          tapply(veg$R, veg$Transect, mean)

-          tapply (x = veg$R, INDEX = veg$Transact, FUN = mean)

o    splits the data of the first variable, based on levels of the second variable

 

the sapply and lapply functions

-          laborious if we wish to calculate mean of large number of variables

-          example

o    20 numerical variables in vegetation dataset

o    sapply(veg[,5:9, FUN = mean)

-          differences

o    tapply

§  calculates mean (or other function) for subsets of observations of a variable

o    lapply / sapply

§  calculate mean etc of one / more variables, using all observations

§  difference

·         presentation of output

o    lapply – presented as list

o    sapply – gives it as vector

 

 

summary function

 

 

-          argument – can be

o    variable

o    output from cbind function

o    data frame

-          example

o    z <- cbind(veg$R, veg$ROCK, veg$LITTER)

o    colnames(z) <- c("R", "ROCK", "LITTER")

o    summary(z)

-          example

o    summary(veg[, c("R", "ROCK", "LITTER"(])

-          example

o    summary(veg[, c(5,6,7)])

 

 

 

Table Function

 

-          observations per farm

o    table(Deer$Farm)

-          observations per year, by sex

o    table(Deer$Sex,Deer$Year)