Efficient Data Manipulation with Loop Functions in R: A Deep Dive into apply and mapply

The Beginner’s Guide to Loop Functions in R:

In addition to lapply and sapply, R also has apply and mapply, which are other loop functions that are commonly used for data manipulation and analysis. In this blog post, we'll explain what these functions are, how they work, and provide some practice material for beginners to intermediate level.

apply: 

Apply a Function to a Matrix or Array

apply is a loop function in R that applies a function to either rows or columns of a matrix or array. Here's the basic syntax:

apply(matrix/array, margin, function)

The matrix/array argument is the matrix or array you want to apply the function to, and the margin argument specifies whether you want to apply the function to rows or columns. margin = 1 applies the function to rows, while margin = 2 applies the function to columns. The function argument is the function you want to apply. For example, let's say we have a matrix of numbers and we want to apply the sum function to each row:

my_matrix <- matrix(c(1, 2, 3, 4, 5, 6), nrow = 2) 

apply(my_matrix, 1, sum)

This will return a vector of the sums of each row in my_matrix.

mapply: 

Apply a Function to Multiple Vectors

mapply is a loop function in R that applies a function to multiple vectors, where the function takes multiple arguments. Here's the basic syntax:

mapply(function, vector1, vector2, ...)

The function argument is the function you want to apply, and the vector1, vector2, etc. arguments are the vectors you want to apply the function to. For example, let's say we have two vectors of numbers and we want to apply the sum function to each corresponding pair of elements:

vector1 <- c(1, 2, 3) 

vector2 <- c(4, 5, 6) 

mapply(sum, vector1, vector2)

This will return a vector of the sums of each corresponding pair of elements in vector1 and vector2.

Practice Material

Here are some exercises to practice using apply and mapply:

• Use apply to apply the mean function to each column of a matrix. For example, the matrix matrix(c(1, 2, 3, 4, 5, 6), nrow = 2) should return the vector c(2.5, 3.5, 4.5).

• Use mapply to apply the sum function to each corresponding pair of elements in three vectors. For example, the vectors c(1, 2, 3), c(4, 5, 6), and c(7, 8, 9) should return the vector c(12, 15, 18).

• Use apply to apply the sd function to each row of a matrix. For example, the matrix matrix(c(1, 2, 3, 4, 5, 6), nrow = 2) should return the vector c(1.5, 1.5).

• For more practice you should start swirl's lessons in R Programming. Complete download process of swirl and R Programming is here, click on the link!

• You can look in to the practice and reading material that is provided in the text book, click here to download the textbook.

• Lecture slides can be downloaded from here. It would be great if you go through them too.

In conclusion, apply and mapply are loop functions in R that are used for data manipulation and analysis. apply applies a function to either rows or columns of a matrix or array, while mapply applies a function to multiple vectors, where the function takes multiple arguments. Both functions can be useful for simplifying code and performing operations on multiple elements at once. By understanding the basic syntax and usage of these functions, data analysts and programmers can greatly enhance their productivity and efficiency in R programming.