###Lesson 1 code###

#Chunk 1#
q()                     # Quits R (important if you use R without a GUI)
?command_name           # Calls up the manual for a command (try ?q())
getwd()                 # Shows the working directory
setwd("directory_name") # Sets the working directory

#Chunk 2#
###Write and run this chunk of code directly in the console
2
2 + 2
a
a <- 3
a
a + 2

#Chunk 3#
###Write this chunk of code in an R script
###This is a comment###
2     #I can write comments wherever I want
2 + 2 #Sum of two numbers 
b
b <- 5 # Assigning a value to an object
b

#Chunk 4#
x <- 1
y <- 2
z <- 10
Peter <- x + y
Bernard <- y - x
Rabbit <- z * Peter

#Chunk 5#
typeof(x)

#Chunk 6#
word <- "hello"
word2 <- "A?7Fd"
mv <- NA
Bool <- TRUE

#Chunk 7#
mode(x)
mode(sin)
mode(word)
mode(Peter)

#Chunk 8#
v1 <- c(1,2,3,4)

#Chunk 9#
v2 <- c("a", 1, 2, 3)
mode(v2)
str(v2)

#Chunk 10#
d <- c(1, 2, 3, TRUE)
e <- c("a", 2, 3, TRUE)

#Chunk 11#
v3 <- c(v1, v1, v1)
v3

#Chunk 12#
rep(4, 6)       # The first argument gives the object to repeat, the second argument the number of repetitions
seq(2, 4, 0.5)  # Consists of values with distance 0.5 from 2 to 4 (including 2 and 4)
1:7             # A vector consisting of 1,...,7
seq(along = v2) # Vector (1,...,length(v2))

#Chunk 13#
length(v2)
class(v2)
mode(v2)
summary(v2)
str(v2)
mean(v2)
var(v2)

#Chunk 14#
v1 <- 1:5
mode(v1)
v1 + 5

#Chunk 15#
v1[1]        # The first entry of the vector
v1[1] + 5    # The first entry of the vector increased by 5
v1[c(1, 2)]  # The first two entries of the vector
v1[-c(1, 2)] # All entries of the vector apart from the first two
v1[v1<3]     # All entries smaller than 3

#Chunk 16#
logicv1 <- (v1>1) & (v1<4)
v1[logicv1]

#Chunk 17#
v4 <- -7:3   # Defines v4 as the vector (−7, −6, ..., 1, 2, 3). Note the blank!
which(v4>0) # Gives the positions of all entries of v4 bigger than 0

#Chunk 18#
v1[1] <- 100
v1[1]
v1

#Chunk 19#
matrix1 <- matrix(c(1, 2, 3, 4), nrow = 2, byrow = TRUE) # Ordered by rows
matrix2 <- matrix(c(1, 2, 3, 4), nrow = 2,byrow = FALSE) # Ordered by columns
D <- diag(2)
matrix3 <- matrix(c(1, 2, 3, 4), nrow = 2, ncol = 4, 
                  byrow = TRUE)

#Chunk 20#
matrix1[1,2] # Accesses the entry in the 1st row, 2nd column
matrix1[ ,1] # Accesses the first column
matrix1[1, ] # Accesses the first row

#Chunk 21#
colnames(matrix1) <- c("A","B")  # Assign names to the columns of matrix1
rownames(matrix1) <- c("C", "D") # Assign names to the rows of matrix1
matrix1
matrix1["C","D"]
matrix1[,"B"]

#Chunk 22#
v3 <- c(1, 1)       # Defines a 2-dimensional vector
t(matrix1)          # Transposes matrix1 (switches rows with columns)
matrix1 %∗% matrix2 # Multiplies matrix1 with matrix 2
matrix1 %∗% v3      # Multiplies matrix with vector
solve(matrix1)      # Inverts the matrix
solve(matrix1, v3)  # Solves the system of linear equation matrix1*x=v3
cbind(matrix1, v3)  # Adds v3 as a new column (works also adding matrices)
rbind(matrix1, v3)  # Adds v3 as a new row (works also adding matrices)