安裝所需的包：
install.packages("xxxx")

載入包：
library("xxxx")

顯示/改變工作文件夾
getwd()/setwd("d:/temp")

文件操作：
1.讀取csv文件
var=read.csv("demo.csv",header=FALSE)——header表示是否有表頭。默覺得TRUE

2.讀取數據文件
data=read.table("demo.data")

3.讀取文本文件
var=readLines("demo.txt",encoding="UTF-8")

4.輸出csv文件
write.csv(var,"var.csv")

5.輸出普通文本文件
write(var,"var.txt")

6.把整個執行空間保存到文件
save.image("demo.RData")

7.讀取文件到執行空間
load("demo.RData")

清除執行空間所有變量：
rm(list=ls())

字符串操作：
1.獲取字符串長度
nchar("asdf")——與length是不同的

2.連接字符串
paste("abc","def")——默認用空格間隔。若取消間隔。可用參數sep=""

3.切割字符串
str1=strsplit("abc def"," ")——切割結果是list類型，如需轉成向量使用str1=unlist(strsplit("abc def"," "))

4.字符串截取
substr("hello",2,3)——參數表示起止位置

5.字符串替代
gsub("a","c","asdfasdf")——把asdfasdf替換成csdfcsdf

6.字符串匹配
grep("oo",c("hello","world","good"))——搜索給定字符串中的特定表達式 。返回其位置索引

集合（向量）操作：
1.求交集
intersect(c("a","b","c"),c("a","c","d"))

2.求並集
union(c("a","b","c"),c("a","c","d"))

3.求差集
setdiff(c("a","b","c"),c("a","c","d"))

4.向量去重
unique(c("a","b","a","c"))

5.向量排序
sort(c("a","b","a","c"))/rev(sort(c("a","b","a","c")))

R語言筆記