Week 1-4 In class activities

a = rep (1,6)

a = seq(1,6)
a[2]

## [1] 2

a[c(2,4)]

## [1] 2 4

a[1:3]

## [1] 1 2 3

x = matrix(1:15, nrow=3)

x = matrix(1:15,nrow=3)
x[,4]

## [1] 10 11 12

x[,3]

## [1] 7 8 9

x[2:3,1:3]

##      [,1] [,2] [,3]
## [1,]    2    5    8
## [2,]    3    6    9

cells = c(1,26,24,68)
rnames = c("R1","R2")
cnames = c("C1","C2")
m = matrix(cells,nrow=2,ncol=2,byrow=TRUE,dimnames=list(rnames,cnames))

d = c(7,9,5,20)
e = c("red","white","red",NA)
f = c(TRUE,TRUE,TRUE,FALSE)
mydata = data.frame(d,e,f)
colnames(mydata) = c("ID", "Color","Status")

mydata[,2:3]

##   Color Status
## 1   red   TRUE
## 2 white   TRUE
## 3   red   TRUE
## 4  <NA>  FALSE

mydata[,c("ID","Color")]

##   ID Color
## 1  7   red
## 2  9 white
## 3  5   red
## 4 20  <NA>

mydata$ID

## [1]  7  9  5 20

mylist <- list(name="Fred",my.numbers=a,my.matrix=x,age=5.3)
mylist[[2]]

## [1] 1 2 3 4 5 6

mylist[["my.numbers"]]

## [1] 1 2 3 4 5 6

class(m)

## [1] "matrix" "array"

class(x)

## [1] "matrix" "array"

for (i in 1:5){print(i)}

## [1] 1
## [1] 2
## [1] 3
## [1] 4
## [1] 5

mat = matrix(sample(100,50),nrow=10)
for (i in 1:10){
  m3=mean(mat[i,])
  print(m3)}

## [1] 42.8
## [1] 60.8
## [1] 44.6
## [1] 45.2
## [1] 27
## [1] 41.2
## [1] 39.6
## [1] 55.4
## [1] 40
## [1] 45.8

for (i in 1:nrow(mat)){
  if(mat[i,2] == "girl"){
    print(mat[i,])
  }
}

calcu = function(a,b){
  result = (a + b *  5) ^ 2
  return(result)
}
calcu(4,2)

## [1] 196

calcu(0.5,0.1)

## [1] 1

y <- matrix(c(1,2,3,4),nrow=2,ncol=2)
y

##      [,1] [,2]
## [1,]    1    3
## [2,]    2    4

y <- matrix(nrow=2,ncol=2)
y[1,1] <- 1
y[2,1] <- 2
y[1,2] <- 3
y[2,2] <- 4
y

##      [,1] [,2]
## [1,]    1    3
## [2,]    2    4

m <- matrix(c(1,2,3,4,5,6),nrow=2,byrow = T)
m

##      [,1] [,2] [,3]
## [1,]    1    2    3
## [2,]    4    5    6

3*y

##      [,1] [,2]
## [1,]    3    9
## [2,]    6   12

y+y

##      [,1] [,2]
## [1,]    2    6
## [2,]    4    8

y <- matrix(0, nrow = 3, ncol = 2)
replacement_matrix <- matrix(c(1, 8, 2, 5), nrow = 2, byrow = TRUE)
y[c(1, 3), ] <- replacement_matrix
print(y)

##      [,1] [,2]
## [1,]    1    8
## [2,]    0    0
## [3,]    2    5

y[-2,]

##      [,1] [,2]
## [1,]    1    8
## [2,]    2    5

x[x[,2]>=3,]

##      [,1] [,2] [,3] [,4] [,5]
## [1,]    1    4    7   10   13
## [2,]    2    5    8   11   14
## [3,]    3    6    9   12   15

m <- matrix(c(1, 2, 3, 4, 5, 6), ncol = 2)
a <- m[(m[, 1] > 1) & (m[, 2] > 5), ]
a

## [1] 3 6