R Conditional Statements

R language provides the following types of conditional statements:

• if statement

• if...else statement

• switch statement

if statement

An if statement consists of a boolean expression followed by one or more statements.

The syntax format is as follows:

if(boolean_expression) {
　　　　//　statements to be executed if the boolean expression is true
}

If the boolean expression boolean_expression is true, execute the code inside here, if it is false, do not execute.

x　<-　50L
if(is.integer(x)) {
　　　print("X is an integer"
}

Execute the above code, and the output result is:

[1] "X is an integer"

if...else statement

An if statement can be followed by an optional else statement, which is executed when the boolean expression is false.

The syntax format is as follows:

if(boolean_expression) {
　　　　//　statements to be executed if the boolean expression is true
}　else　{
　　　　//　statements to be executed if the boolean expression is false
}

If the boolean expression boolean_expression is true, execute the code within the if block. If the boolean expression is false, execute the code within the else block.

x　<-　if("weibo" %in% x) {3codebox,"taobao")
if("w"3codebox " %in% x) {
　　　print("Contains w"3codebox)
}　else　{
　　　print("Does not contain w"3codebox)
}

Execute the above code, and the output result is:

[1] "contains w"3codebox"

if there are multiple condition checks, you can use if...else if...else:

else if( boolean_expression　1) {
　　　　//　if the boolean expression boolean_expression　1　statements to be executed if true
}　2) {
　　　　//　if the boolean expression boolean_expression　2　statements to be executed if true
}　3) {
　　　　//　if the boolean expression boolean_expression　3　statements to be executed if true
}　else　{
　　　　//　execute the statements when all boolean expressions are false
}

x　<-　if("weibo" %in% x) {3codebox,"taobao")
print("The first if contains weibo"
　　　else if ("w"
}3codebox " %in% x) {
　　　print("The second if contains w"3codebox)
}　else　{
　　　print("Not found")
}

Execute the above code, and the output result is:

[1]　"The second if contains w3codebox"

switch statement

A switch statement allows testing the situation when a variable equals multiple values. Each value is called a case.

The syntax format is as follows:

switch(expression,　case1,　case2,　case3....)

switch The statement must follow the following rules:

• switch In the statement expression It is a constant expression, which can be an integer or a string. If it is an integer, it returns the corresponding case position value. If the integer is not within the range of positions, it returns NULL.

• If multiple values match, the first one is returned.

• expressionIf it is a string, it corresponds to the value of the variable name in the case, and if there is no match, there is no return value.

• switch does not have a default parameter available.

The following example returns the third value:

x　<-　switch(
　　　3,
　　　"google",
　　　"w3codebox",
　　　"taobao",
　　　"weibo"
)
print(x)

Execute the above code, and the output result is:

[1]　"taobao"

If it is a string, it returns the value corresponding to the string variable:

you.like<-"w3codebox"
switch(you.like,　google="www.google.com",　w3codebox　=　"www.oldtoolbag.com",　taobao　=　"www.taobao.com")

Execute the above code, and the output result is:

[1]　"www.oldtoolbag.com"

If the integer is not within the range, it returns NULL

>　x　<-　switch(4,"google","w3codebox,"taobao")
>　x
NULL
>　x　<-　switch(4,"google","w3codebox,"taobao")
>　x
NULL