第六章 分支
3 > 2 # 3比2大?是真(true)的。
1 > 2 # 1比2大?是假(false)的。
!(1 > 2) # 1不比2大?呃......
3 > 2 & 1 > 2 # 3比2大,并且1比2大?假的。
3 > 2 | 1 > 2 # 3比2大,或者1比2大吗?真的。
3 > 2 & !(1 > 2) # 3比2大,并且1不比2大?好像是真的吧...
x <- 1:3
x == 2
x == 2 | x == 3
y <- c(4, 1, 2)
x > y
x > y & y > 1
TRUE * FALSE
TRUE + TRUE
sum(x > y)
x %in% y
x[x %in% y]
which(x %in% y)
Y[N > 100][1]
x <- 60
if(x < 75) print("x is less than 75")
if(x < 75) {
print("x is less than 75")
y <- x + 10
print(y)
}
x <- 60
if(x < 75) {
print("x is less than 75")
} else {
print("x is larger than 75")
} # 如果(),那么{},否则{}。
x <- 60
if(x < 75) {
print("small")
} else if(x > 90){
print("large")
} else {
print("good")
}
ifelse(x < 75, "small", ifelse(x > 90, "large", "good"))
N <- numeric(100)
N[1] <- 66.8
for(t in 1:99) N[t + 1] <- N[t] + r * N[t]
Y <- seq(2008, length.out = 100)
plot(x = Y + 2007, y = N, xlab = "Year", ylab = "Population",
cex = ifelse(N >= 100, 2, 1), pch = 16, type = "b",
col = ifelse(N >= 100, "red", "darkgreen"))