sense.
Definitions are not always rigorous definitions as a mathematician would be used to. We rather use practical definitions (e.g. how a function is implemented).
The use of a function is – mainly at the beginning of the book – highlighted as follows. For example:
Function use for mean()
mean (x, na.rm = FALSE, trim = 0, …)
Where
x is an R-object,
na.rm is a boolean (setting this to TRUE will remove missing values),
trim is the fraction of observations to be removed on both sides of the distribution before the mean is computed – the default is 0 and it cannot be higher than 0.5
From this example, it should be clear how the function mean() is used. Note the following:
The name of the function is in the title.
On the first line we repeat the function with its most important parameters.
The parameter x is an obligatory parameter.
The parameter na.rm can be omitted. When it is not provided, the default FALSE is used. A parameter with a default can be recognised in the first line via the equal sign.
The three dots indicate that other parameters can be passed that will not be used by the function mean(), but they are passed on to further methods.
Some functions can take a lot of parameters. In some cases, we only show the most important ones.
Later on in the book, we assume that the reader is able to use the examples and find more about the function in its documentation. For example, ?mean will display information about the function mean.
When a new concept or idea is built up with examples they generally appear just like that in the text. Additional examples after the point is made are usually highlighed as follows:
Example: Mean
An example of a function is mean(), as the name suggests it calculates the arithmetic mean (average) of data fed into the function.
# First, generate some data: x <- c(1,2,3) # Then calculate the mean: mean(x) ## [1] 2
Some example environments are split in two parts: the question and the solution as follows:
Example: Mean
What is the mean of all integer numbers from one to 100? Use the function mean().
mean(1:100) ## [1] 50.5
There are a few more special features in the layout that might be of interest.
A hint is something that adds additional practical information that is not part of the normal flow of the text.
When first studying a section, skip the hints, and when reading it a second time paymore attention to the hints.
When we want to draw attention to something that might or might not be clear from the normal flow of the text, we put it in a “notice environment.” This looks as follows:
Note that hints, notes and warnings look all similar, but for your convenience, we have differentiating colours and layout details.
There are more such environments and we let them speak for themselves.
Digression – This is good to know
A digression does what you would expect from it. It is not necessary to read in order to understand the rest of the chapter. However, it provides further insight that is useful to gain a deeper insight of the subject discussed.
Skip the digressions when you read the text first, and come back to them later.
When reading the book, always read the comments in the code.
# Code and especially the comments in it are part of # the normal flow of the text!
In general, a warning is important to read once you will start working on your own.
Note that the boxes with a shadow are “lifted off the page” and are a little independent from the flow of the main text. Those that are no shadow are part of the main flow of the text (definitions, examples, etc.)
Notes
1 1 You, will of course, first have to install the base software R. More about this in Chapter 4 “The Basics of R” on page 21.
2 2 The number sign, #, is also known as the “hash sign” or “pound sign.” It probably evolved from the “libra ponda” (a pound weight). It is currently used in any different fields as part of phone numbers, in programming languages (e.g. in an URL it indicates a sub-address, in R it precedes a comment, etc), the command prompt for the root user in Unix and Linux, in set theory (#S is the cardinality of the set S), in topology (A#B is the connected sum of manifolds A and B), number theory (#n is the primorial of n), as keyword in some social media, etc. The pronunciation hence varies widely: “hash” when used to tag keywords (#book would be the hash sign and the tag book). Hence, reading the “#”-sign as “hashtag” is at least superfluous). Most often, it is pronounced as “pound.” Note that the musical notation is another symbol, <, that is pronounced as “sharp” as in the music (e.g. C<).
3 3 ISO standards refer to the standards published by the International Organization for Standardization (ISO). This is an international standard-defining body, founded on 23 February 1947, it promotes worldwide proprietary, industrial and commercial standards. At this point, 164 countries are member and decisions are made by representatives of those countries. ISO is also recognised by the United Nations.
