R語言資料結構2—matrix
矩陣
矩陣是一個二維陣列，只是每個元素都擁有相同的模式（數值型、字元型或邏輯型）。可通
過函式matrix建立矩陣。一般使用為：
matrix(vector = , nrow = , ncol = , byrow = ,dimnames = list(,))
其中vector包含了矩陣的元素，nrow和ncol用以指定行和列的維數，dimnames包含了可選的、
以字元型向量表示的行名和列名。選項byrow則表明矩陣應當按行填充（byrow=TRUE）還是按
列填充（byrow=FALSE），預設情況下按列填充。
1.Construction of a matrix 構建一個矩陣
my.matrix <- matrix(1:9,byrow=TRUE,nrow=3)
[,1] [,2] [,3]
[1,] 1 2 3
[2,] 4 5 6
[3,] 7 8 9
# Box office Star Wars: In Millions (!)
# First element: US
# Second element: Non-US
new.hope <- c(460.998007, 314.4)
empire.strikes <- c(290.475067, 247.9)
return.jedi <- c(309.306177, 165.8)
# Construct matrix(通過vector構建矩陣):
star.wars.matrix <- matrix(c(new.hope, empire.strikes, return.jedi), nrow = 3,
byrow = TRUE)
# give names to rows and columns!
#給矩陣命名
colnames(star.wars.matrix) <- c("US", "non-US")
rownames(star.wars.matrix) <- c("A new hope", "The empire strikes back", "Return of the Jedi")
#打印出矩陣
# Print the matrix to the console:
star.wars.matrix
US non-US
A new hope 460.9980 314.4
The empire strikes back 290.4751 247.9
Return of the Jedi 309.3062 165.8
#計算出row的和
worldwide.vector <- rowSums(star.wars.matrix)
# Print worldwide revenue per movie
worldwide.vector
A new hope The empire strikes back
Return of the Jedi
775.4 538.4 475.1
# Bind the new variable total.per.movie as a column to star.wars
#通過連線兩個矩陣構建新矩陣
all.wars.matrix <- cbind(star.wars.matrix, worldwide.vector)
all.wars.matirx
US non-US
worldwide.vector
A new hope 461.0 314.4 775.4
The empire strikes back 290.5 247.9 538.4
Return of the Jedi 309.3 165.8 475.1
#構建票價矩陣
ticket.prices.matrix <- matrix(c(5, 7, 6, 8, 7, 9), nrow = 3, byrow = TRUE,
dimnames = list(movie.names, col.titles))
visitors <- star.wars.matrix/ticket.prices.matrix
average.us.visitor <- mean(visitors[, 1])
average.non.us.visitor <- mean(visitors[, 2])
visitors
average.us.visitor
average.non.us.visitor
visitors
US non-US
A new hope 92.20000 44.91429
The empire strikes back 48.41667 30.98750
Return of the Jedi 44.18571 18.42222
>average.us.visitor
[1] 61.60079
>average.non.us.visitorverage.non.us.visitor
[1] 31.44134