Data Science Specialization - course 2 - 2

OBJETIVE
It is to be able to make use of the cache memory to store values that have a high cost of calculation process.

DESCRIPTION
For this task we will use two functions; makeVector and cachemean, the first one will serve us to make a calculation and the second function will serve us to store the value and later to be able to recover it.

The term “Lexical Scope” defines a set of rules that the compiler uses to find a variable that has been defined in the programming algorithm. In practice it is to be able to locate where the variables are set and their scope.

An example:

function foot(a){ # 1 ambit

var b = a * 2;        # 2 scope  
function bar(c){      # 3 ambito  
    print(a, b, c);  
}  
bar(b * 3);           # 2 ambit

}

We execute the function by passing it a parameter = 2
foot(2);

the answer after executing the foot function is: 2, 4, 12

TASKS

makeVector <- function(x = numeric()) {
        m <- NULL
        set <- function(y) {
                x <<- y
                m <<- NULL
        }
        get <- function() x
        setmean <- function(mean) m <<- mean
        getmean <- function() m
        list(set = set, get = get,
             setmean = setmean,
             getmean = getmean)
}

cachemean <- function(x, ...) {
        m <- x$getmean()
        if(!is.null(m)) {
                message("getting cached data")
                return(m)
        }
        data <- x$get()
        m <- mean(data, ...)
        x$setmean(m)
        m
}

We run a calculation, example:

a <- makeVector(1:1000);
cachemean(a);
## [1] 500.5
b <- cachemean(a);
## getting cached data
b
## [1] 500.5

Conclusion
We have seen a practical example of the use of cache memory.