#章节1 新手入门
getwd()
setwd("D:/R")
setwd("D:R")
library("MASS")
?mean
??"mean"
?mean
q()
#章节2.1基础数学
sqrt(x=9) #计算非负值的平方根
2^(2 1)-4 64^((-2)^(2.25-1/4)) #-2要加括号
log(x=243,base=3) #对数
exp(x=3) #指数
#练习
(6*2.3 42)/(3^(4.2-3.62))
sqrt((mean(25.2,12,16.44,15.3,18.6))/2)
log(x=0.3,base=exp(1)) #exp(1)=e=2.718
-0.00000000423546322 #-4.235463e-09
exp(log(x=0.3,base=exp(1)))
#章节2.2分配对象
x<--5
x=x 1
mynumber=45.2
y<-mynumbe
ls() #查看当前工作空间所包含的内容
#练习
x<-(3^2)*(4^(1/8))
x<-x/2.33
y<--8.2*(10^(-13))
x*y
#章节2.3向量
myvec<-c(1,3,1,42) #创建向量
myvec
foo<-32.1
myvec2<-c(3,-3,2,3,45,1e 03,64^0.5,2 (3-1)/9.44,foo)
myvec2
myvec3<-c(myvec,myvec2)
myvec3
#序列
3:27 #从3开始逐项加1到27为止
foo<-5.3
bar<-foo:(-47 1.5) #从5.3开始逐项减1
ba
seq(from=3,to=27,by=3) #序列函数seq
seq(from=3,to=27,length.out=40) #40个等间隔的数
myseq<-seq(from=foo,to=(-47 1.5),by=-2.4) #递减序列
myseq
myseq2<-seq(from=foo,to=(-47 1.5),length.out=5)
myseq2
rep(x=1,times=4) #重复函数rep
rep(x=c(3,62,8.3),times=3) #times的值为重复x的次数
rep(x=c(3,62,8.3),each=2) #each的值为重复元素的个数
rep(x=c(3,62,8.3),times=3,each=2)
foo<-4
c(3,8.3,rep(x=32,times=foo),seq(from=-2,to=1,length.out=foo 1))
sort(x=c(2.5,-1,-10,3.44),decreasing=FALSE) #排序函数sort
sort(x=c(2.5,-1,-10,3.44),decreasing=TRUE)
foo<-seq(from=4.3,to=5.5,length.out=8)
foo
bar<-sort(x=foo,decreasing=TRUE)
ba
sort(x=c(foo,bar),decreasing=FALSE)
length(x=c(3,2,8,1)) #长度函数length
length(x=5:13)
foo<-4
bar<-c(3,8.3,rep(x=32,times=foo),seq(from=-2,to=1,length.out=foo 1))
length(x=bar)
#练习
x<-seq(from=5,to=-11,by=-0.3)
x
x<-sort(x,decreasing=FALSE)
x
x2<-sort(rep(x=c(-1,3,-5,7,-9),times=2,each=10),decreasing=FALSE)
x2
length(x2)
x<-seq(from=6,to=12)
y<-rep(x=5.3,times=3)
z<-c(seq(from=6,to=12),rep(x=5.3,times=3),-3,seq(from=102,to=100,length.out=9))
length(z)
#2.3.3子集和元素的提取
myvec<-c(5,-2.3,4,4,4,6,8,10,40221,-8)
length(myvec)
myvec[1]
foo<-myvec[2]
foo
myvec[length(x=myvec)]
myvec.len<-length(x=myvec)
bar<-myvec[myvec.len-1]
ba
1:myvec.len
myvec[-1]
baz<-myvec[-2]
baz
qux<-myvec[-(myvec.len-1)]
qux
c(qux[-length(x=qux)],bar,qux[length(x=qux)])
length(x=qux)
qux[-length(x=qux)]
bar<-myvec[myvec.len-1]
ba
qux[length(x=qux)]
myvec[c(1,3,5)]
1:4
foo<-myvec[1:4]
foo
length(x=foo):2
foo[length(foo):2]
indexes<-c(4,rep(x=2,times=3),1,1,2,3:1)
indexes
foo[indexes]
bar<-c(3,2,4,4,1,2,4,1,0,0,5)
ba
bar[1]<-6
ba
bar[c(2,4,6)]<-c(-2,-0.5,-1) #用向量替换多个元素的值
ba
bar[7:10]<-100
ba
#练习
x<-seq(from=3,to=6,length.out=5)
x
y<-rep(x=c(2,-5.1,-33),times=2)
y
z<-7/42 2
z
x<-c(x,y,z)
x
x1<-x[c(1,5)]
x3<-x[-c(1,5)]
x4<-c(x1,x3)
sort(x=x,decreasing=FALSE)
x5<-sort(x=x,decreasing=FALSE)
x6<-x5[5:1] #使用冒号作为索引颠倒顺序
x6
x7<-c(rep(x=x3[4],times=3),rep(x=x3[6],times=4),rep(x=x3[10],times=1))
x7
x8<-sort(x=x,decreasing=FALSE)
x8[c(1,5:7,12)]<-c(99:95)
x8
