Author: saqibkhan

To aggregate data in R, we use the aggregate() function. This function has the following essential parameters, in this order:

• x—the data frame to aggregate.
• by—a list of the factors to group by.
• FUN—an aggregate function to compute the summary statistics for each group (e.g., mean, max, min, count, sum).

1. For loop—iterates over a sequence the number of times equal to its length (unless the statements break and/or next are used) and performs the same set of operations on each item of that sequence. This is the most common type of loops. The syntax of a for loop in R is the following:

for (variable in sequence) {
operations
}Powered By 

2. While loop—performs the same set of operations until a predefined logical condition (or several logical conditions) is met—unless the statements break and/or next are used. Unlike for loops, we don’t know in advance the number of iterations a while loop is going to execute. Before running a while loop, we need to assign a variable (or several variables) and then update its value inside the loop body at each iteration. The syntax of a while loop in R is the following:

variable assignment

while (logical condition) {
operations
variable update
}Powered By 

3. Repeat loop—repeatedly performs the same set of operations until a predefined break condition (or several break conditions) is met. To introduce such a condition, a repeat loop has to contain an if-statement code block, which, in turn, has to include the break statement in its body. Like while loops, we don’t know in advance the number of iterations a repeat loop is going to execute. The syntax of a repeat loop in R is the following:

repeat { 
operations 
if(break condition) {
    break
}
}

• A variable name can be a combination of letters, digits, dots, and underscores. It can’t contain any other symbols, including white spaces.
• A variable name must start with a letter or a dot.
• If a variable name starts with a dot, this dot can’t be followed by a digit.
• Reserved words in R (TRUE, for, NULL, etc.) can’t be used as variable names.
• Variable names are case-sensitive.

1. Using the assignment operator <-, e.g., my_var <- 1—the most common way of assigning a value to a variable in R.
2. Using the equal operator =, e.g., my_var = 1—for assigning values to arguments inside a function definition.
3. Using the rightward assignment operator ->, e.g., my_var -> 1—can be used in pipes.
4. Using the global assignment operators, either leftward (<<-) or rightward (->>), e.g., my_var <<- 1—for creating a global variable inside a function definition.

• ggplot2—the most popular R data visualization package allowing the creation of a wide variety of plots.
• Lattice—for displaying multivariate data as a tiled panel (trellis) of several plots.
• Plotly—for creating interactive, publication-quality charts.
• highcharter—for easy dynamic plotting, offers many flexible features, plugins, and themes; allows charting different R objects with one function.
• Leaflet—for creating interactive maps.
• ggvis—for creating interactive and highly customizable plots that can be accessed in any browser by using Shiny’s infrastructure.
• patchwork—for combining several plots, usually of various types, on the same graphic.

To create a user-defined function in R, we use the keyword function and the following syntax:

function_name <- function(parameters){
function body 
}Powered By 

1. Function name—the name of the function object that will be used for calling the function after its definition.
2. Function parameters—the variables separated with a comma and placed inside the parentheses that will be set to actual argument values each time we call the function.
3. Function body—a chunk of code in the curly brackets containing the operations to be performed in a predefined order on the input arguments each time we call the function. Usually, the function body contains the return() statement (or statements) that returns the function output, or the print() statement (or statements) to print the output.

An example of a simple user-defined function in R:

my_function <- function(x, y){
return(x + y)
}