Welcome to R Square

# 对向量 for 循环

# 计算x^2
x = c(1, 2, 3)
for (i in x) {
print(i^2)
}
## [1] 1
## [1] 4
## [1] 9

# 九九乘法表
for (j in 1:9) {
for (i in 1:j) {
m = i * j
cat(i, "*", j, "=", m, " ")
}
cat("\n")
}
## 1 * 1 = 1
## 1 * 2 = 2  2 * 2 = 4
## 1 * 3 = 3  2 * 3 = 6  3 * 3 = 9
## 1 * 4 = 4  2 * 4 = 8  3 * 4 = 12  4 * 4 = 16
## 1 * 5 = 5  2 * 5 = 10  3 * 5 = 15  4 * 5 = 20  5 * 5 = 25
## 1 * 6 = 6  2 * 6 = 12  3 * 6 = 18  4 * 6 = 24  5 * 6 = 30  6 * 6 = 36
## 1 * 7 = 7  2 * 7 = 14  3 * 7 = 21  4 * 7 = 28  5 * 7 = 35  6 * 7 = 42  7 * 7 = 49
## 1 * 8 = 8  2 * 8 = 16  3 * 8 = 24  4 * 8 = 32  5 * 8 = 40  6 * 8 = 48  7 * 8 = 56  8 * 8 = 64
## 1 * 9 = 9  2 * 9 = 18  3 * 9 = 27  4 * 9 = 36  5 * 9 = 45  6 * 9 = 54  7 * 9 = 63  8 * 9 = 72  9 * 9 = 81


# 对非向量的 for 循环

# 分别对矩阵u和v执行线性回归
u = matrix(c(1, 2, 3, 1, 2, 4), ncol = 2)
v = matrix(c(8, 12, 20, 15, 10, 2), ncol = 2)
for (m in c("u", "v")) {
z = get(m)
fit = lm(z[, 2] ~ z[, 1])
print(fit)
}
##
## Call:
## lm(formula = z[, 2] ~ z[, 1])
##
## Coefficients:
## (Intercept)       z[, 1]
##     -0.6667       1.5000
##
##
## Call:
## lm(formula = z[, 2] ~ z[, 1])
##
## Coefficients:
## (Intercept)       z[, 1]
##      23.286       -1.071


# for - next 语句

# 编程序计算1+2+3+4+6+7的值
x = 1:7
sum = 0
for (i in x) {
if (i == 5)
next
sum = sum + i
}
print(sum)
## [1] 23


# while 循环

i = 1
while (i <= 10) {
i = i + 4
}
print(i)
## [1] 13


# while 和 break 语句

i = 1
while (TRUE) {
i = i + 4
if (i > 10)
break
}
print(i)
## [1] 13


# repeat 和 break 语句

i = 1
repeat {
i = i + 4
if (i > 10)
break
}
print(i)
## [1] 13


# if - else 语句

# 如果x = 2，则y = x，否则y = x + 1
x = 3
if (x == 2) {
y = x
} else {
y = x + 1
}
print(y)
## [1] 4


# switch 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"


# 编写函数

# 编写函数(统计奇数个数)
oddcount = function(x) {
k = 0
for (i in x) {
if (i%%2 == 1)
k = k + 1
}
return(k)
}

# 测试函数
x = 1:10
oddcount(x)
## [1] 5