R Notebook

1. Read in the weight data that is posted on webpage as ‘Weight data’.

wtData<-read.table("http://www.uvm.edu/~bbeckage/Teaching/DataAnalysis/Data/wts.txt",header=TRUE)
head(wtData)

2. What type of object is the file read in as? If it is not a data frame, coerce it to one.

class(wtData)

[1] "data.frame"

3. What are object/data types of each of the columns?

str(wtData)

'data.frame':   15 obs. of  3 variables:
 $ gender    : Factor w/ 2 levels "f","m": 2 2 2 1 1 2 1 1 1 1 ...
 $ height_in : int  72 67 68 64 66 69 68 63 65 69 ...
 $ weight_lbs: int  165 160 160 114 135 148 120 138 135 150 ...

4. Plot weight (on y axis) vs height (on x axis) with different colored symbols for each gender.

plot(wtData[wtData$gender=='f',]$height_in, wtData[wtData$gender=='f',]$weight_lbs,
     col="red",xlim=range(wtData$height_in),ylim=range(wtData$weight_lbs), ylab="Wt",xlab="Ht")
points(wtData[wtData$gender=='m',]$height_in,wtData[wtData$gender=='m',]$weight_lbs,col="blue",pch=2)

library(lattice)
xyplot(height_in~weight_lbs|gender,data=wtData)

detach("package:lattice", unload=TRUE)

library(ggplot2)
qplot(height_in, weight_lbs, data = wtData, colour = gender)

detach("package:ggplot2",unload=TRUE)

library(ggplot2)
a<-ggplot(wtData, aes(x=height_in, y=weight_lbs))
a + geom_point(aes(color=factor(gender)))

  
detach("package:ggplot2",unload=TRUE)

5. Write a function to calculate ‘10!’, i.e., 10 factorial (1098…1). Show the result for 10 and 20.

myFactorial<-function(x){
  if(identical(x,0)) return(1)
  myProd<-1 
  for(i in x:1){ # this causes the index i to vary from 1 to 10
    myProd<-myProd*i
    cat(paste("i= ",i,"; myProd= ",myProd,sep=""),fill=T) 
    # print(myProd)
  }
  return(myProd)
  # cat(paste("index= ",i,"; myProd= ",myProd,sep=""),fill=T) 
}
myFactorial(0)

[1] 1

myFactorial(1)

i= 1; myProd= 1
[1] 1

myFactorial(3)

i= 3; myProd= 3
i= 2; myProd= 6
i= 1; myProd= 6
[1] 6

myFactorial(4)

i= 4; myProd= 4
i= 3; myProd= 12
i= 2; myProd= 24
i= 1; myProd= 24
[1] 24

myFactorial(3)

Called from: myFactorial(3)

i

[1] 3

myProd

[1] 3

Q

myFactorial2<-function(x){
  if(identical(x,0)) return(1)
  return(tail(cumprod(1:x),1))
}
myFactorial2(0)

[1] 1

myFactorial2(1)

[1] 1

myFactorial2(3)

[1] 6

myFactorial2(4)

[1] 24

myFactorial3<-function(x){
  if(identical(x,0)) return(1)
  return(x * myFactorial3(x-1))
}
myFactorial3(0)

[1] 1

myFactorial3(1)

[1] 1

myFactorial3(3)

[1] 6

myFactorial3(4)

[1] 24

Timing the functions:

library(microbenchmark)
microbenchmark(myFactorial(10))

Unit: nanoseconds
            expr min   lq     mean median     uq     max neval
 myFactorial(10) 991 1015 32739.34 1066.5 1094.5 3167358   100

microbenchmark(myFactorial2(10))

Unit: microseconds
             expr   min    lq     mean median     uq    max neval
 myFactorial2(10) 8.943 9.266 10.09731 9.4625 9.6465 62.448   100

microbenchmark(myFactorial3(10))

Unit: microseconds
             expr   min     lq    mean median     uq    max neval
 myFactorial3(10) 6.117 6.4255 6.69957  6.584 6.7385 17.854   100

detach("package:microbenchmark",unload=TRUE)

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