2. 控制流
重复和循环
for
for (i in 范围){循环体}
for (i in 1:10) {
print("hahaha")
}
>>>
[1] "hahaha"
[1] "hahaha"
[1] "hahaha"
[1] "hahaha"
[1] "hahaha"
[1] "hahaha"
[1] "hahaha"
[1] "hahaha"
[1] "hahaha"
[1] "hahaha"
while
while (condition){循环体}
i <- 0
while (i < 3) {
print("hahahha")
i <- i + 1 #i+=1
}
>>>
[1] "hahahha"
[1] "hahahha"
[1] "hahahha"
【循环练习：斐波那契】
f <- rep(0, 100)
f[1] <- 1
f[2] <- 1
for (i in 3:100) {
f[i] <- f[i - 1] + f[i - 2]
print(f[i])
}
f <- rep(0, 100)
f[1] <- 1
f[2] <- 1
i <- 3
while (i <= 100) {
f[i] <- f[i - 1] + f[i - 2]
print(f[i])
i <- i + 1
}
条件执行
If
if(condition) 执行语句
if(condition1) 执行语句1 else 执行语句1
if(condition1) 执行语句1 else if(condition2) 执行语句2 else 执行语句3
#格式一
grades <- c(66, 32, 58, 99)
for (i in 1:length(grades)) {
if (grades[i] > 60) print("AAA") else print("BBB")
}
#格式二
grades <- c(66, 32, 58, 99)
for (i in 1:length(grades)) {
if (grades[i] > 60) {
print("AAA")
} else {
print("BBB")
}
}
switch
switch根据一个表达式的值选择语句执行
switch(expr, ...) # ... 表示与expr的各种可能输出值绑定的语句
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 = "Cheer up",
angry = "Calm down now"
)
)
>>>
[1] "Cheer up"
[1] "There is nothing to fear"
