a=factor(letters[1:10])
a[3]="w"
a=as.character(a)
a[3]="w"
a;factor(a)





x=scan()
1.5 2.6 3.7 2.1 8.9 12 -1.2 -4
x=c(1.5,2.6,3.7,2.1,8.9,12,-1.2,-4)
w=read.table(file.choose(),header=T)
setwd("f:/mydata")
(x=rnorm(20))
write(x,"test.txt")
y=scan("test.txt")
(y)
y=iris;y[1:5,];str(y)
write.table(y,"test.txt",row.names=F)
w=read.table("test.txt",header=T)
str(W)
write.csv(y,"test.csv")
v=read.csv("test.csv")
(v)
str(v)
data=read.table("clipboard")
(data)






(z=seq(-1,10,length=100))
(z=seq(-1,10,len=100))
(z=seq(10,-1,-0.1))
(x=rep(1:3,3))
(x=rep(3:5,1:3))
x=rep(c(1,10),c(4,5))
w=c(1,3,x,z);w[3]
(w)
x=sample(1:100,12);x
all(x>0);any(x>0);(1:10)[x>0]
diff(x)
diff(x,lag=2)
x=matrix(1:20,4,5);x
x=matrix(1:20,4,5,byrow=T);x
a=t(x)
a[2,3]
nrow(x);ncol(x);dim(x)
x=matrix(rnorm(24),4,6)
x
x[c(2,1),];x[,c(1,3)]
x[x[,1]>0,1]
sum(x[,1]>0)
x[,-c(1,3)]
diag(x)
diag(1:5)
diag(5)
apply(x,2,sum)
apply(x,1,mean)
x[x[,1]>0&x[,3]<=1,1]
x=array(runif(24),c(4,3,2));x
is.matrix(x)
dim(x)