What is lazy evaluation and how is it helpful in R
This recipe explains what is lazy evaluation and how is it helpful in R
Recipe Objective
Lazy evaluation also known as call by need is a technique where the expression's evaluation is delayed until it's value is absolutely needed. In other words, it's used to avoid repeated evluations.
Lazy evaluation is used in R as it increases the efficiency of the program when used interatively. This is done by making sure that only necessary objects are loaded in memory or looked for. One disadvantage is that it can make a program less predictable.
In this recipe we will see how lazy evaluation works in R with an example of a function
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Table of Contents
STEP 1: Create a function to evaluate mean of a vector
mean_of_vector = function(a, mean_ = mean(a)){
a = a[!is.na(a)]
print(a)
paste("The mean of a is ", mean_)
}
STEP 2: Call the function
mean_of_vector(c(20,30,40,50,NA,60,NA))
[1] 20 30 40 50 60
'The mean of a is 40'
Note: In this example the the function changes the value of a before passing it to the mean_ function. If mean_ was evaluated as soon as the function was called then the value of mean_ would have been NA. This is Lazy evaluation.
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