基本結構展示：
if (7<10) {
print("Seven is less than ten")
} else{
print("seven is more than ten")
}
實例演示：
Titanic=read.csv("https://goo.gl/4Gqsnz") #從網絡讀取數據
1. any() #any代表只要有任一值符合，即爲TRUE
if (any(titanicC$Age>70)) {
print("there are passengers older than 70")
} else{
print("no one is older than 70")
}
2. all() #所有都滿足才true
if (all(titanicC$Age>10)) {
print("all passengers older than 10")
} else{
print("there are passengers younger than 10")
}
3. na.omit() #放的位置決定是刪除單一變量缺失值，還是刪除任何變量缺失值
if (any(na.omit(titanic$Age==100))) {
print("there are passengers aged 100")
} else{
print("there are no passengers aged 100")
} #數據庫中只要有missing的記錄都刪掉
if (any(titanic$Age==80, na.rm=TRUE)) {
print("there are passengers aged 80")
} else{
print("there are no passengers aged 80")
} #Age這個變量有missing的記錄刪掉，其他變量有missing可以保留
4. else if 寫更重複的語句
x=100
y=10
if(x<y){
print("AA")
} else if(x==y){
print(BB)
} else{
print(CC)
}