Cheat Sheet

• >

  R code gets executed.
• +

  R code is waiting for more.
• The meaning of: *, /, +, -, ^, ==, !=

  Multiplication, Divide, Addition, Subtraction, To the power of, Equal to, Not equal to
• Placing a question mark before a function switches the bottom right window to the help tab.
• <-

  Assigns a value to a named object. Called arrow.

  Can also work with "=", but run into problems with this later when trying to use functions that require the use of "=".
• # inside a code chunk

  Makes that line a comment, so R will ignore that line. Comments are useful for reminding yourself of what your code is doing.  
• # outside a code chunk

  Outside a code chunk it creates headings. ## would make a subheading, and so on and so forth with the more "#" used.
• Named objects are case sensitive.
• What does the dim() function do?

  Can find out how many rows and columns there are for the data.
• What do str() function or glimpse() function do?

  Get a glimpse at the data.
• What are reserved words?

  Are a set of words that you can't use as names, but R will tell you if you make the mistake of trying to name a variable after one of these.
• R code is conducted in the “Console”.

  However, R code can be carried out somewhere else before sent to the console.
• Where is the console?

  Bottom left window
• Where is the Environment and what does it do?

  Top right window, and shows everything that is stored in R.
• How to run a code chunk, and why it needs to be done:

  Enter what required in the new R script. Hit Ctrl + Enter on the top line, or alternatively hit “Run”.

  Each line must be “entered” or “ran”, otherwise R doesn’t know what (e.g.) y means.
• Where is the editor and what does it do?

  Top left hand window, where you write and edit code
• The bottom-right window shows the plots that you create, the files in your project, and other functions.
• R Packages:

  We can install packages, but to actually use the package we need to use library().

  To install: install.packages()
• To store a sequence of numbers into R (as seen singularly with arrow), we combine the values using the combine function ( c ) and give the sequence a name.
• A sequence of elements all of the same type is called a vector
• Vectors can also be words, as long as they are all of the same type
•  R markdown: information

  Combines the analytical power of R and the utility of a text-processor. Can produce a report, containing all our analysis and written text, without having to copy results over to a Word document. Essentially involves normal written text embedded with “code-chunks”. The document can then be made into a PDF or HTML.
• In the environment you can check what class something in the environment is stored as.
• Ways of achieving different text styles in a report:

  ^2^ makes it small and high.

  ~~text~~ for strikethrough

  Embolden = **text** or __text__

  Italicise = *text* or _text_
• To declare something as a factor use factor().

  e.g. mydata$Degree <- factor(mydata$Degree)
• Double (dbl) and numeric (num) are terms for numbers.
• What do you use $ for?

  To specify a column within a dataset.
• What is the purpose of [ , ]?

  To show a distinct point in a data set.

  i.e. [3,4] shows you the value in the 3rd row and 4th column.

  Just the 3rd row = [3,]

  4th column = [,4]

  Can change the value in [3,4] using the arrow.
• Can add a new column using $ and the arrow to specify what is in that column. Number in the list has to match the number of rows.
• Can use list() instead of c()
• For a summary of the data:

  summary()

  min()

  max()
• What is a factor in R?

  A factor in R is a data structure that is used to store and categorize categorical data, which are variables that take on a limited number of different values. Factors can store both integers and strings, and have a levels attribute that holds all the possible values of the factor.
• Factorise and show the "somevariable" variable in the "somedata" dataframe

  as.factor(somedata$somevariable)
• theme(axis.text.x = element_text(angle = 45, vjust = 1, hjust=1))

  Add (+) this on to the end of a ggplot() function if you want to rotate the x-axis labels 45 degrees, or 90 degrees, so that they don’t overlap.