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?matrix a <- matrix(data=NA, nrow=5, ncol=5, byrow=T) a <- matrix(data=1:25, nrow=5, ncol=5) a v1 <- 1:5 v2 <- 5:1 cbind(v1, v2) rbind(v1, v2) nrow(a) ncol(a) t(a) matrix(1,2,3) seq(2,9) seq(4,10, by=2) seq(3,30, length=9) rep(2,4) rep(c(1,2), 4) rep(c(1,2), c(4,4)) rep(1:4,2) rep(1:4, rep(3,4)) # Bai 7 x <- matrix(data=c(3,2,-1,1), nrow=2, ncol=2, byrow=T) x y <- matrix(data=c(1,4,0,0,1,-1), nrow=2, ncol=3, byrow=T) y 2*x x*x x%*%x # matrix multiplication x%*%y t(y) # transpose matrix solve(x) ?solve chiaHetA <- function(a, n) { return(sum(c(1:n) %% a == 0)) } chiaHetA(4,50) # Bai tap week 2 # 1/ sum <- function(x) { res <- 0 for (i in x) res <- res + i return(res) } x <- 1:5 sum(x) # 5/ phanvi <- function(x, p) { sort(x) i <-p * length(x) / 100 # if (round(i) == i) { # return((x[i] + x[i+1]) / 2) # } else { # return(round(i)) # } return(if (round(i) == i) (x[i] + x[i+1]) / 2 else round(i)) } x <- 100:1 x ?runif x <- runif(100) phanvi(x, 2) hist(x) boxplot(x) #-------------- setwd('E:/R lab') data <- read.csv('E:/R lab/DataExcel.csv') attach(data) T1 stem(T1) TanSoT1 <- table(T1) names(TanSoT1) [TanSoT1==max(TanSoT1)] max(TanSoT1) median(T1) mean(T1) range(T1) # ~= max(T1) - min(T1) quantile(T1, probs=c(0.25, 0.5, 0.75)) quantile(T1, probs=seq(0,1,0.25)) var(T1) sd(T1) # Do lech chuan ~= sqrt(var(T1)) sqrt(var(T1) / abs(mean(T1))) # He so bien thien boxplot(T1) boxplot(T1~KV,data=data,main="Diem toan HK1") KVinGT <- table(KV,GT) KVinGT barplot(KVinGT) plot(T1,T2) cor(T1,T2) # He so tuong quan cov(T1,T2) # Hiep phuong sai plot(T1,V1) cor(T1,V1) cov(T1,V1) plot(T1,N1) cor(T1,N1) cov(T1,N1)