Object types
Vectors (1D)
Definition: numeric or character
myVec <- 1:10; names(myVec) <- letters[1:10]
myVec[1:5]
## a b c d e
## 1 2 3 4 5
myVec[c(2,4,6,8)]
## b d f h
## 2 4 6 8
myVec[c("b", "d", "f")]
## b d f
## 2 4 6
Factors (1D)
Definition: vectors with grouping information
factor(c("dog", "cat", "mouse", "dog", "dog", "cat"))
## [1] dog cat mouse dog dog cat
## Levels: cat dog mouse
Matrices (2D)
Definition: two dimensional structures with data of same type
myMA <- matrix(1:30, 3, 10, byrow = TRUE)
class(myMA)
## [1] "matrix"
myMA[1:2,]
## [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
## [1,] 1 2 3 4 5 6 7 8 9 10
## [2,] 11 12 13 14 15 16 17 18 19 20
myMA[1, , drop=FALSE]
## [,1] [,2] [,3] [,4] [,5] [,6] [,7] [,8] [,9] [,10]
## [1,] 1 2 3 4 5 6 7 8 9 10
Data Frames (2D)
Definition: two dimensional objects with data of variable types
myDF <- data.frame(Col1=1:10, Col2=10:1)
myDF[1:2, ]
## Col1 Col2
## 1 1 10
## 2 2 9
Arrays
Definition: data structure with one, two or more dimensions
Lists
Definition: containers for any object type
myL <- list(name="Fred", wife="Mary", no.children=3, child.ages=c(4,7,9))
myL
## $name
## [1] "Fred"
##
## $wife
## [1] "Mary"
##
## $no.children
## [1] 3
##
## $child.ages
## [1] 4 7 9
myL[[4]][1:2]
## [1] 4 7
Functions
Definition: piece of code
myfct <- function(arg1, arg2, ...) {
function_body
}
Subsetting of data objects
(1.) Subsetting by positive or negative index/position numbers
myVec <- 1:26; names(myVec) <- LETTERS
myVec[1:4]
## A B C D
## 1 2 3 4
(2.) Subsetting by same length logical vectors
myLog <- myVec > 10
myVec[myLog]
## K L M N O P Q R S T U V W X Y Z
## 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26
(3.) Subsetting by field names
myVec[c("B", "K", "M")]
## B K M
## 2 11 13
(4.) Subset with $ sign: references a single column or list component by its name
iris$Species[1:8]
## [1] setosa setosa setosa setosa setosa setosa setosa setosa
## Levels: setosa versicolor virginica