Some useful functions for working with objects in R

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In this post, we will introduce and provide several useful and important functions in R. Most of them are fairly basic, and frequently used in data analysis with R programming.

length() – get the length of an object

#to show first three observations of a data frame 'grade'
head(grade,3)
  StudentID        Fullname Race Gender Country Age Math Physics
1         1     James Zhang    A   Male      US  23   73      70
2         2       Wilson Li    E Female      UK  26   95      76
3         3 Richard Nuan Ye    A   Male      UK  35   77      83
  Chemistry       Date
1        87 10/31/2008
2        83  3/16/2008
3        92  5/22/2008
#length of data frame 'grade'
length(grade)
[1] 10
#to create a vector
test<-grade$Age
#length of a vector
length(test)
[1] 20

dim() – to show the dimension of an object

#dimension of a data frame
dim(grade)
[1] 20 10

str() – to show structure of a data frame

str(grade)
'data.frame':	20 obs. of  10 variables:
 $ StudentID: chr  "1" "2" "3" "4" ...
 $ Fullname : chr  "James Zhang" "Wilson Li" "Richard Nuan Ye" "Mary Deng" ...
 $ Race     : chr  "A" "E" "A" "E" ...
 $ Gender   : chr  "Male" "Female" "Male" "Female" ...
 $ Country  : chr  "US" "UK" "UK" "US" ...
 $ Age      : num  23 26 35 21 19 43 37 28 19 25 ...
 $ Math     : num  73 95 77 60 77 79 87 95 73 66 ...
 $ Physics  : num  70 76 83 99 89 64 99 87 92 93 ...
 $ Chemistry: num  87 83 92 84 93 83 67 93 84 65 ...
 $ Date     : chr  "10/31/2008" "3/16/2008" "5/22/2008" "1/24/2009" ...

class() – to show class type of an object

#class of a data frame
class(grade)
[1] "data.frame"
#class of an vector 
class(test)
[1] "numeric"

mode() – to show the mode(data storage type) of an object

#mode of a data frame
mode(grade)
[1] "list"
#mode of a vector 
mode(test)
[1] "numeric"

names() – to show the names of an object

#names of columns of a data frame
names(grade)
 [1] "StudentID" "Fullname"  "Race"      "Gender"    "Country"  
 [6] "Age"       "Math"      "Physics"   "Chemistry" "Date" 

c() – Combine extra elements to a vector

test2<-c(test, 20, 20)  
test2
 [1] 23 26 35 21 19 43 37 28 19 25 42 32 27 35 21 29 36 39 24 25 20
[22] 20

cbind() – Combines data frames across columns

#to create a data frame of 3 columns
gradepart<-grade[,c(7:9)]
names(gradepart)<-c("v1","v2","v3")
#combine two data frames
test3<-cbind(grade,gradepart )
#show first 3 observations of the combined data frame
head(test3,3)
  StudentID        Fullname Race Gender Country Age Math Physics
1         1     James Zhang    A   Male      US  23   73      70
2         2       Wilson Li    E Female      UK  26   95      76
3         3 Richard Nuan Ye    A   Male      UK  35   77      83
  Chemistry       Date v1 v2 v3
1        87 10/31/2008 73 70 87
2        83  3/16/2008 95 76 83
3        92  5/22/2008 77 83 92
> 

rbind() – Combines data frames across rows

#to create a new data frame of 10 rows
test4<-grade[1:10,]
#combine two data frame along rows
test5<-rbind(grade, test4)
#show first 15 observations of the combined data frame 
head(test5,15)
     StudentID        Fullname Race Gender Country Age Math Physics
1          1     James Zhang    A   Male      US  23   73      70
2          2       Wilson Li    E Female      UK  26   95      76
3          3 Richard Nuan Ye    A   Male      UK  35   77      83
4          4       Mary Deng    E Female      US  21   60      99
5          5    Jason Wilson    A   Male      UK  19   77      89
6          6 Jennifer Hopkin    A Female      UK  43   79      64
7          7    Kari Gjendem    E Female      US  37   87      99
8          8     Wenche Dale    E Female      US  28   95      87
9          9     Jane Larsen    A Female      US  19   73      92
10        10  Steinar Hansen    A   Male      US  25   66      93
11        11    Michael Chen    A   Male      UK  42   83      90
12        12    Josef Curton    E   Male      US  32   71      63
13        13  Jennifer Jones    E   Male      US  27   79      76
14        14      Gary Grant    E Female      UK  35   90      78
15        15        Phil Yao    A   Male      UK  21   69      69
   Chemistry       Date
1         87 10/31/2008
2         83  3/16/2008
3         92  5/22/2008
4         84  1/24/2009
5         93  7/30/2009
6         83   4/5/2009
7         67 11/24/2008
8         93  10/2/2008
9         84   6/5/2009
10        65   8/1/2008
11        77 10/24/2008
12        96  11/8/2009
13        82 10/29/2008
14        92 10/24/2008
15        83 10/15/2008

seq() – to create a sequence of numbers into a vector

#generate a vector from 1 to 10
seq(1,10)     
 [1]  1  2  3  4  5  6  7  8  9 10
#generate a vector of 5 numbers between 1 and 10, gap 2
seq(1,10,2) 
[1] 1 3 5 7 9

rep() – generate a sequence of number with repetition

#generate a vector 1,1,1,1,1
rep(1,5)    
[1] 1 1 1 1 1
#generate a vector 1,2,1,2,1,2,1,2,1,2 
rep(c(1,2),5)
 [1] 1 2 1 2 1 2 1 2 1 2

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