Finally some statistics...

Try to do the following. What is remarkable about the behavior? How can we find out what happens here?

# draw plots of two datasets ?
plot(AirPassengers)
plot(swiss)

Hint: What are the differences between both objects from an R perspective?

plot() is a generic: It has multiple methods each of which is specific to a particular class.

# show some (just for presentation reasons 
# you should try it without the index)
# methods of plot
methods(plot)[c(2,4,15,26)]

[1] "plot.data.frame" "plot.default"    "plot.lm"         "plot.ts"        

Note: You can look at a functions source code by just calling the function without parentheses ().

From scatterplots, histograms to quantiles and t.tests: Example

1. functions
2. factors (categorical variables)
3. apply family
4. …

You can define your own function by

fname <- function(arg1,arg2){
  res <- arg1+arg2
  res # last argument equal to return(res)
}

And call it by

fname(1,2) # returns 3

[1] 3

load("../data/mlb.RData")
# position is a factor, i.e. a categorical var.
class(mlb$position)

[1] "factor"

levels(mlb$position) # reference level is usually the first level

[1] "Catcher"           "Designated_Hitter" "First_Baseman"    
[4] "Outfielder"        "Relief_Pitcher"    "Second_Baseman"   
[7] "Shortstop"         "Starting_Pitcher"  "Third_Baseman"    

levels(relevel(mlb$position,"Starting_Pitcher"))

[1] "Starting_Pitcher"  "Catcher"           "Designated_Hitter"
[4] "First_Baseman"     "Outfielder"        "Relief_Pitcher"   
[7] "Second_Baseman"    "Shortstop"         "Third_Baseman"    

apply a function over a list or vector and return a list or vector.

# do not run
lapply(somelist,function(element_of_list) do_something(element_of_list))

sapply(somelist,function(element_of_list) do_something(element_of_list))

see also: apply(), tapply(), mapply().

• What did you consider useful?
• Are there any applications you want to see?
• Are there any dataset that you want to explore? e.g. google trends, twitter, seminar papers, datasets from psychology?