R语言入门学习笔记4_r语言rep函数 factor-优快云博客

本文深入探讨了R语言中的矩阵代数运算，包括基本的加减乘除、幂运算，以及复杂的矩阵乘法、转置、求逆等操作。同时，介绍了如何计算矩阵的列均值、列和、行均值、行和，并展示了如何创建和操作对角矩阵。此外，还讲解了因子函数的应用，如基于因子进行分组统计。

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# 1. Matrix Algebra
set.seed(123)
A=matrix(sample(100,15),nrow = 5,ncol = 3)
set.seed(234)
B=matrix(sample(100,15),nrow = 5,ncol = 3)
set.seed(321)
X=matrix(sample(100,4),nrow = 2,ncol = 2)
set.seed(213)
b=matrix(sample(100,15),nrow = 5,ncol = 1)

# + - * / ^
A+2
A*2
A^2

# Matrix multiplication
t(A)%*%B # 转置的A矩阵乘以B

# Return a vector containing the column means of A
colMeans(A)

# Return a vector containing the column sums of A
colSums(A)

# Return a vector containing the row means of A
rowMeans(A)

# Return a vector containing the row sums of A
rowSums(A)

# Matrix Crossproduct
# A'A
crossprod(A)
# A'B
crossprod(A,B)

# Inverse of A where A is a square matrix
solve(X)

# Sloves for vector x in the equation b=Ax
# a=Xv
a=matrix(1:4,nrow = 2,ncol = 2)
v=solve(X,a)
v

# Returns a vector containing the elements of the principal diagnoal
diag(X)

# Creates a diagonal matrix with the elements of x in the principal diagonal
diag(c(1,2,3,4))

# If k is a scalar,this creates a k×k identity matrix
diag(5)

# Eigenvalues and eigenvectors of A
eigen(X)

# 2. Factor
Factor=factor(rep(c(1:3),times=5))
Factor
X=sample(100,15)
tapply(X, Factor, mean)
rbind(X,Factor)
boo=rbind(X,Factor)[2,]==2
which(boo)
rbind(X,Factor)[1,which(boo)]
sum(rbind(X,Factor)[1,which(boo)])/length(which(boo))