课程源代码：https://github.com/miwu8512/IntroToR

视频地址： https://www.youtube.com/watch?v=rPj5FsTRboE&list=PLBTcf4SwWEI9_kCOJ-1o-Jwr-_Qb6bkeg

Lecture 3

1 List

> x = matrix(1:20,nrow=5,ncol=4,byrow=TRUE)
> swim = read.csv("http://www.macalester.edu/~kaplan/ISM/datasets/swim100m.csv")
> mylist = list(swim,x)
> mylist[2]
[[1]]
      [,1] [,2] [,3] [,4]
[1,]    1    2    3    4
[2,]    5    6    7    8
[3,]    9   10   11   12
[4,]   13   14   15   16
[5,]   17   18   19   20

> mylist[[2]][2]  ##用[[]]申明所用的list
[1] 5
> mylist[[2]][1:2]
[1] 1 5
> mylist[[2]][1:2,3]
[1] 3 7
> mylist[[2]][1:2,]
      [,1] [,2] [,3] [,4]
[1,]    1    2    3    4
[2,]    5    6    7    8

2 Operators 判断语句

, >=, <, <=, ==, !=, x|y(x或y), x&y(x和y)

3 Control flow 流程控制

3.1 repetition and looping 循环语句

Looping constructs repetitively execute a statement or series of statments until a condition is not true. Including the for and while structures.

> #For-loop
> for(i in 1:10){
  +   print(i)
  + }
[1] 1
[1] 2
[1] 3
[1] 4
[1] 5
[1] 6
[1] 7
[1] 8
[1] 9
[1] 10

> #While-loop
> i=1
> while(i<=10){
+   print(i)
+   i=i+1
+ }
[1] 1
[1] 2
[1] 3
[1] 4
[1] 5
[1] 6
[1] 7
[1] 8
[1] 9
[1] 10

• for 和while运行速度慢，大数据量时尽量避免使用，尽量用向量和方程解决

3.2 Conditional execution 条件语句

In conditonal execution, a statement or statements are only executed if a specified condition is met. Including if, if-else, switch.

> #If statement
> i=1
> if(i == 1){
+   print("Hello World")
+ }
[1] "Hello World"

> #If-else statement
> i=2
> if(i == 1){
+   print("Hello World")
+ }else{
+   print("Goodbye World")
+ }
[1] "Goodbye World"

> #Switch statement
> feelings = c("sad","afraid")
> for(i in feelings){
+   print(
+     switch(i,
+            happy = "I am glad you are happy",
+            afraid = "There is nothing to fear",
+            sad = "Chear up",
+            angry = "Calm down now"
+     )
+   )
+ }
[1] "Chear up"
[1] "There is nothing to fear"

4 User-defined Function 自定义函数

One of the greatest strengths of R is the ability to add functions. In fact, many of the functions in R are functions of existing functions.

> myfunction = function(x,a,b,c){
+   return(a*sin(x)^2-b*x+c)
+ }
> curve(myfunction(x,20,3,4),xlim=c(1,20))
> myfeeling = function(x){
+   for(i in x){
+     print(
+       switch(i,
+              happy = "I am glad you are happy",
+              afraid = "There is nothing to fear",
+              sad = "Chear up",
+              angry = "Calm down now"
+              )
+       )
+     }
+   }
> feelings = c("sad","afraid")
> myfeeling(feelings)
[1] "Chear up"
[1] "There is nothing to fear"