R语言数据结构2—matrix

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矩阵

矩阵是一个二维数组，只是每个元素都拥有相同的模式（数值型、字符型或逻辑型）。可通

过函数matrix创建矩阵。一般使用为：

matrix(vector = , nrow = , ncol = , byrow = ,dimnames = list(,))

其中vector包含了矩阵的元素，nrow和ncol用以指定行和列的维数，dimnames包含了可选的、

以字符型向量表示的行名和列名。选项byrow则表明矩阵应当按行填充（byrow=TRUE）还是按

列填充（byrow=FALSE），默认情况下按列填充。

1.Construction of a matrix 构建一个矩阵

my.matrix <- matrix(1:9,byrow=TRUE,nrow=3)

      [,1] [,2] [,3]
[1,]    1    2    3
[2,]    4    5    6
[3,]    7    8    9

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# 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(通过vector构建矩阵):

star.wars.matrix <- matrix(c(new.hope, empire.strikes, return.jedi), nrow = 3,

byrow = TRUE)

# give names to rows and columns!

#给矩阵命名

colnames(star.wars.matrix) <- c("US", "non-US")

rownames(star.wars.matrix) <- c("A new hope", "The empire strikes back", "Return of the Jedi")

#打印出矩阵

# 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

#计算出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

#通过连接两个矩阵构建新矩阵

all.wars.matrix <- cbind(star.wars.matrix, worldwide.vector)

#print

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

#构建票价矩阵

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

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