第二课

c(2,5,6,2,9)

## [1] 2 5 6 2 9

c("a","f","md","c")

## [1] "a"  "f"  "md" "c"

1:5

## [1] 1 2 3 4 5

rep("x",times=3)

## [1] "x" "x" "x"

seq(from=3,to=21,by=3)

## [1]  3  6  9 12 15 18 21

rnorm(n=3)

## [1]  0.4295305 -0.9886426 -0.6427203

paste0(rep("x",times=3),1:3)

## [1] "x1" "x2" "x3"

x<-c(1,3,5,1)
x=c(1,3,5,1)
x+1

## [1] 2 4 6 2

log(x)

## [1] 0.000000 1.098612 1.609438 0.000000

sqrt(x)

## [1] 1.000000 1.732051 2.236068 1.000000

x>3

## [1] FALSE FALSE  TRUE FALSE

x==3

## [1] FALSE  TRUE FALSE FALSE

max(x) #最大值

## [1] 5

min(x) #最小值

## [1] 1

mean(x) #均值

## [1] 2.5

median(x) #中位数

## [1] 2

var(x) #方差

## [1] 3.666667

sd(x) #标准差

## [1] 1.914854

sum(x) #总和

## [1] 10

length(x) #长度

## [1] 4

unique(x) #去重复

## [1] 1 3 5

duplicated(x) #对应元素是否重复

## [1] FALSE FALSE FALSE  TRUE

table(x) #重复值统计

## x
## 1 3 5 
## 2 1 1

sort(x)

## [1] 1 1 3 5

sort(x,decreasing = F)

## [1] 1 1 3 5

sort(x,decreasing = T)

## [1] 5 3 1 1

x = c(1,3,5,1)
y = c(3,2,5,6)
x == y 

## [1] FALSE FALSE  TRUE FALSE

y == x

## [1] FALSE FALSE  TRUE FALSE

x + y

## [1]  4  5 10  7

paste(x,y,sep=",")

## [1] "1,3" "3,2" "5,5" "1,6"

paste(x,y)

## [1] "1 3" "3 2" "5 5" "1 6"

#当两个向量长度不一致
x = c(1,3,5,6,2)
y = c(3,2,5)
x == y # 啊！warning！

## [1] FALSE FALSE  TRUE FALSE  TRUE

#循环补齐--看ppt
a = c(1,2)
b = c(1,2,3)
a+b

## [1] 2 4 4

a == b

## [1]  TRUE  TRUE FALSE

#利用循环补齐简化代码
paste0(rep("x",3),1:3)

## [1] "x1" "x2" "x3"

paste0("x",1:3)

## [1] "x1" "x2" "x3"

intersect(x,y)

## [1] 3 5 2

union(x,y)

## [1] 1 3 5 6 2

setdiff(x,y)

## [1] 1 6

setdiff(y,x)

## numeric(0)

x %in% y #x的每个元素在y中存在吗

## [1] FALSE  TRUE  TRUE FALSE  TRUE

y %in% x #y的每个元素在x中存在吗

## [1] TRUE TRUE TRUE

x <- 8:12
#根据逻辑值取子集
x[x == 10]

## [1] 10

x[x < 12]

## [1]  8  9 10 11

x[x %in% c(9,13)]

## [1] 9

#根据位置取子集
x[4]

## [1] 11

x[2:4]

## [1]  9 10 11

x[c(1,5)]

## [1]  8 12

x[-4]

## [1]  8  9 10 12

x[-(2:4)]

## [1]  8 12

####2.5.修改向量中的某个/某些元素：取子集+赋值
x

## [1]  8  9 10 11 12

#改一个元素
x[4] <- 40
x

## [1]  8  9 10 40 12

#改多个元素
x[c(1,5)] <- c(80,20)
x

## [1] 80  9 10 40 20

x[x%in%y]

## numeric(0)

#### 2.6 简单向量作图
k1 = rnorm(12);k1

##  [1]  0.4078494  1.8536021  0.6923547 -1.8542915 -1.2391541  0.5122553
##  [7] -1.1694122  0.7246900  0.3466781  0.2286454 -0.6850314 -0.4258046

k2 = rep(c("a","b","c","d"),each = 3);k2

##  [1] "a" "a" "a" "b" "b" "b" "c" "c" "c" "d" "d" "d"

plot(k1)

boxplot(k1~k2)

summary(cars)

##      speed           dist       
##  Min.   : 4.0   Min.   :  2.00  
##  1st Qu.:12.0   1st Qu.: 26.00  
##  Median :15.0   Median : 36.00  
##  Mean   :15.4   Mean   : 42.98  
##  3rd Qu.:19.0   3rd Qu.: 56.00  
##  Max.   :25.0   Max.   :120.00