The goal of this tutorial is to learn how to define default values for parameters in a handmade function.
# In this example we will use the open repository of plants classification Iris.
data("iris")
summary(iris)## Sepal.Length Sepal.Width Petal.Length Petal.Width
## Min. :4.300 Min. :2.000 Min. :1.000 Min. :0.100
## 1st Qu.:5.100 1st Qu.:2.800 1st Qu.:1.600 1st Qu.:0.300
## Median :5.800 Median :3.000 Median :4.350 Median :1.300
## Mean :5.843 Mean :3.057 Mean :3.758 Mean :1.199
## 3rd Qu.:6.400 3rd Qu.:3.300 3rd Qu.:5.100 3rd Qu.:1.800
## Max. :7.900 Max. :4.400 Max. :6.900 Max. :2.500
## Species
## setosa :50
## versicolor:50
## virginica :50
##
##
## # The way to define a function is always
# myfunction <- function(parameters){}
# Let's create a function to sum all the members of a vector and divide the sum by 5
sumanddivide <- function(my_vector, my_number){
result <- sum(my_vector)/my_number
return(result)
}
sumanddivide(iris$Sepal.Length, 5)## [1] 175.3# However we could define a default value for the denominator
sumanddivide <- function(my_vector, my_number = 5){
result <- sum(my_vector)/my_number
return(result)
}
# And now this should be the default value that we get when we don't specify the second parameter
sumanddivide(iris$Sepal.Length, 5)## [1] 175.3# When we don't specify the denominator we get vector/5
sumanddivide(iris$Sepal.Length)## [1] 175.3# However we can change the value and get any result we want
sumanddivide(iris$Sepal.Length, 10)## [1] 87.65In this tutorial we have learnt how to define default values for the parameters of a function. This could be very useful if we don’t want the user to introduce all the parameters every time he uses the function. It also prevents the function to crash when some parameter is not introduced.