a_integer<- 1
a_double<- 0.1
#整数型与浮点型
is.integer(a_double)
is.double(a_integer)
#1被默认为1.0double型
a_integer<- as.integer(a_integer)
is.integer(a_integer)
#用as.interger改变为整数型

#character
a_character<-"Hello World"
a_num_character<-"123"
#
is.character(a_character)
is.numeric(a_num_character)

a_num_character<-as.numeric(a_num_character)
is.numeric(a_num_character)

paste(a_character,"abc",a_num_character,sep="_")
#sep是paste内部变量，代表间隔符，未输入时默认空格
paste0(a_character," ",a_num_character)
#paste0代表不需要间隔符
substr(a_character,start=1,stop=5)
#从字符串中取出一段字符
paste1<-paste(a_character,"abc",a_num_character,sep="_")