class1.2.Rmd

```{r}
x <- c(1,55,4,89)
y <- x>10
y
```

```{r}
c(-1,0,1)/0
```

```{r}
sample(10)+100 # recycle
```

```{r}
1:9 +1:3
```

```{r}
x[c(1:3)]
x[c(1,3)]
x[x<3]

```
-----------List------------
```{r}
z <- list(a=1:3,b="a str",c =pi,d=list(-1,-5))
str(z)
```

```{r}
x3<-list(1,2,list(2,list(3)))
str(x3)
```
```{r}
str(z[4])
str(z[[4]])
```
Function
```{r}
?mean
```

```{r}
pos_detection<-function(x){
if(x>0){
  print("pos")
}else if(x==0){
  print("zero")
}else{
  print("neg")}
}

pos_detection(-12)
```

```{r}
sum_two <- function(x,y){
  return(x+y)
}

sum_two(2,5)
```

```{r}
f<- function(x){
  x+y
}
f(10)
```