R Fundamentals II

Reference

pdf creates a PDF file (given by argument file) ready for receiving graphics.
Arguments width and heigth define the page size.
par(mfrow = c(nr, nc)) creates a grid to place multiple graphs on a single page, where nr is the number of rows and nc is the number of columns of that grid.
Use graphics functions (e.g. plot, hist, boxplot, abline, text, etc.) to send plots into the file.
Close the opened file by dev.off().
Functions png or jpeg can be used instead of pdf for other file formats.

Put code whose parameters change frequently in a function, then call it with different parameter values to customize its behavior.
Define a function by assigning function(...) to a name, where ... stands for one or more arguments.
Enclose the body of a function into {}.
The last line of a function is returned, or you can use return explictly.
Any code written in the body of the function is isolated to the function when it is called.
Functions can be nested, i.e. they can call other functions.
In a function call, when assigning values to function arguments, you must use = (and not <-).

Use if condition to start a conditional statement and else to provide a default.
Enclose the bodies of the branches of conditional statements into { }, unless the body contains only one line.
Use == to test for equality.
X && Y is only true if both X and Y are TRUE.
X || Y is true if either X or Y, or both, are TRUE.
Zero is considered FALSE; all other numbers are considered TRUE.
Use for if you want to repeat a block of code multiple times with known number of iterations.
Use while if you want to repeat a block of code until a condition is met.
Nest loops to operate on multi-dimensional data.
break breaks out of a loop.
next moves to the nex iterations without finishing the current iteration.