> grades<-read.table('http://www.stat.wmich.edu/naranjo/stat4640/data/Grades.dat',header=F)
>
> ls()          # list objects
[1] "colors" "ev"     "grades" "m1"     "m2"     "x"      "y"      "z"     
>
> # assign variable names
> names(grades)<-c("ID","Sex", "Class", "Quizzes", "Exam1", "Exam2", "Lab", "Final")
> attributes(grades)
$names
[1] "ID"      "Sex"     "Class"   "Quizzes" "Exam1"   "Exam2"   "Lab"    
[8] "Final"  

$class
[1] "data.frame"

$row.names
 [1]  1  2  3  4  5  6  7  8  9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25
[26] 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49

> summary(grades)        # desciptive statistics
       ID     Sex        Class          Quizzes          Exam1       
 air    : 1   f:17   Min.   :2.000   Min.   :20.00   Min.   : 33.00  
 aln    : 1   m:32   1st Qu.:3.000   1st Qu.:41.00   1st Qu.: 71.00  
 bag    : 1          Median :3.000   Median :44.00   Median : 86.00  
 bam    : 1          Mean   :3.449   Mean   :42.84   Mean   : 80.53  
 bec    : 1          3rd Qu.:4.000   3rd Qu.:47.00   3rd Qu.: 95.00  
 bej    : 1          Max.   :4.000   Max.   :50.00   Max.   :100.00  
 (Other):43                                                          
     Exam2             Lab             Final      
 Min.   : 51.00   Min.   : 63.00   Min.   : 74.0  
 1st Qu.: 86.00   1st Qu.: 92.00   1st Qu.:124.0  
 Median : 93.00   Median : 95.00   Median :147.0  
 Mean   : 90.57   Mean   : 93.53   Mean   :139.5  
 3rd Qu.: 98.00   3rd Qu.: 98.00   3rd Qu.:161.0  
 Max.   :100.00   Max.   :100.00   Max.   :191.0  

> summary(grades$Quizzes)
   Min. 1st Qu.  Median    Mean 3rd Qu.    Max. 
  20.00   41.00   44.00   42.84   47.00   50.00 

> summary(grades$Sex)
 f  m 
17 32 

> mean(grades)     
        ID        Sex      Class    Quizzes      Exam1      Exam2        Lab       Final 
        NA         NA   3.448980  42.836735  80.530612  90.571429  93.530612  139.510204 

> sd(grades)
        ID        Sex      Class    Quizzes      Exam1      Exam2        Lab       Final 
        NA         NA  0.5795553  6.5617164 17.5856263 10.1837289  6.8132898  27.7377018 

> attach(grades)

> table(Sex)          # frequency table
Sex
 f  m 
17 32 

> table(Sex,Class)    # two-way frequency table
   Class
Sex  2  3  4
  f  0  7 10
  m  2 16 14

> grades[1:5,]        # print subset (same as matrix)

   ID Sex Class Quizzes Exam1 Exam2 Lab Final
1 air   f     4      50    93    93  98   162
2 aln   m     4      49    95    98  97   175
3 bam   m     4      39    63    84  95    95
4 bag   f     3      46    92    96  88   150
5 bes   f     4      45   100    98  96   191