R If-else语句示例图解

在if语句中, 当条件为true时, 将执行内部代码。如果条件为假, 则将执行if块之外的代码。

还有另一种决策语句, 称为if-else语句。 if-else语句是if语句, 后跟else语句。当布尔表达式为false时, 将执行if-else语句, else语句。简而言之, 如果布尔表达式具有真值, 则执行if块, 否则执行else块。

R编程将任何非零和非空值都视为true, 如果该值是零或null, 则将它们视为false。

If-else语句的基本语法如下：

if(boolean_expression) {
   // statement(s) will be executed if the boolean expression is true.
} else {
   // statement(s) will be executed if the boolean expression is false.
}

流程图

例子1

# local variable definition
a<- 100
#checking boolean condition
if(a<20){
	# if the condition is true then print the following
	cat("a is less than 20\n")
}else{
	# if the condition is false then print the following
	cat("a is not less than 20\n")
}
cat("The value of a is", a)

输出

例子2

x <- c("Hardwork", "is", "the", "key", "of", "success")

if("key" %in% x) {	
   print("key is found")
} else {
   print("key is not found")
}

输出

例子3

a<- 100
#checking boolean condition
if(a<20){
	cat("a is less than 20")
	if(a%%2==0){
		cat(" and an even number\n")
	}
	else{
		cat(" but not an even number\n")
	}
}else{
	cat("a is greater than 20")
	if(a%%2==0){
		cat(" and an even number\n")
	}
	else{
		cat(" but not an even number\n")
	}
}

输出

例子4

a<- 'u'
if(a=='a'||a=='e'||a=='i'||a=='o'||a=='u'||a=='A'||a=='E'||a=='I'||a=='O'||a=='U'){
	cat("character is a vowel\n")	
}else{
	cat("character is a constant")
}
cat("character is =", a)
}

输出

例子5

a<- 'u'
if(a=='a'||a=='e'||a=='i'||a=='o'||a=='u'||a=='A'||a=='E'||a=='I'||a=='O'||a=='U'){
	cat("character is a vowel\n")	
}else{
	cat("character is a constant")
}
cat("character is =", a)
}

输出