num1<-c(9.1,8.2,7.3)
num2<-1:10
char<-c('a','b','c') #单引号or双引号都可以
logit<-c(TRUE,FALSE,T,F)
c(1,'a',TRUE)
sex<-c('F','M','F','M')
sex
sexf<-factor(sex)
sexf
num1[1]<-100 #索引一定要加方括号
num1[c(1,3)]<-c(99.9,77.7)
num1[c(T,F,T)]
num1[-2]
num3<-c('first'=9.1,'second'=8.2,'third'=7.3)
num3[c(1,3)]
num3[c('first','third')]a<-20:30
a%%2
a%%2==0
a[a%%2==0] #找偶数class(num1)
class(char) 
class(logit)
class(sexf)is.character(num1)
as.character(num1)
num1<-as.character(num1)
class(num1)
is.character(char)
is.character(logit)
as.character(logit)
as.logical(c(0,1,2))NA #缺失值
NaN #无意义的数
Inf #正无穷 大写I
-Inf #负无穷 
NULL #不存在 表示参数没有赋值b<-c(NA,0/1,sqrt(-1),1/0,-1/0)
bis.na(b)#把NA和NaN都记为缺失值
is.finite()#查看是不是有限数
is.infinite()#查看是不是无穷#homework Q1
a<-1:100
a#homework Q2
a[1]<-0
a#homework Q3
a<-a[-1:-20]
a#homework Q4
b<-1:100
b[b%%2!=0]#homework Q5
d<-c(1,'abc')
d#homework Q6
class(d)