Now it is time to finally start learning how we can program some sort of logic using R! Our first step in this learning journey for programming will be simple if, else, and else if statements.
Here is the syntax for an if statement in R:
if (condition){
# Execute some code
}
So what does this actually mean if you've never seen an if statement before? It means that we can begin to apply some simple logic to our code. We say if some condition is true then execute the code inside of the curly brackets.
For example, let's say we have two variables, hot and temp. Imagine that hot starts off as FALSE and temp is some number in degrees. If the temp is greater than 80 than we want to assign hot==TRUE.
Let's see this in action:
hot <- FALSE
temp <- 60
if (temp > 80){
hot <- TRUE
}
hot
# Reset temp
temp <- 100
if (temp > 80){
hot <- TRUE
}
hot
Something to keep in mind is that you should format your code carefully so you can come back later on and easily read it! By convention we align the closing bracket with the if statement it refers to. However, because we use brackets we could be sloppy (not good!) and still have the code work out:
if( 1 == 1){ print('hi')}
if(1 == 1)
{
print('hi')
}
# This works...but hard to read!
A good editor like RStudio will help you make sure everything is aligned well.
If we want to execute another block that occurs if the if statement is false, we can use an else statement to do this! It has the syntax:
if (condition) {
# Code to execute if true
} else {
# Code to execute if above was not true
}
Notice the alignment of the curly brackets and the use of the else keyword. Let's see it in action!
temp <- 30
if (temp > 90){
print("Hot outside!")
} else{
print("Its not too hot today!")
}
What if we wanted more options to print out, rather than just two, the if and the else? This is where we can use the else if statement to add multiple condition checks, using else at the end to execute code if none of our conditions match up with and if or else if.
Let's see this in action!
temp <- 30
if (temp > 80){
print("Hot outside!")
} else if(temp<80 & temp>50){
print('Nice outside!')
} else if(temp <50 & temp > 32){
print("Its cooler outside!")
} else{
print("Its really cold outside!")
}
temp <- 75
if (temp > 80){
print("Hot outside!")
} else if(temp<80 & temp>50){
print('Nice outside!')
} else if(temp <50 & temp > 32){
print("Its cooler outside!")
} else{
print("Its really cold outside!")
}
Let's see a final more elaborate example of if,else, and else if to close out our discussion! Let's imagine that we have a store with two items for sale: ham and cheese and we want an automated report to go to HQ depending on how many we sell:
# Items sold that day
ham <- 10
cheese <- 10
# Report to HQ
report <- 'blank'
if(ham >= 10 & cheese >= 10){
report <- "Strong sales of both items"
}else if(ham == 0 & cheese == 0){
report <- "Nothing sold!"
}else{
report <- 'We had some sales'
}
print(report)
This is still relatively simple and can be expanded upon, but we just wanted to show how we could use if, else, and else if along with some logical operators. We'll slowly build up more complex tasks!