Session 3: Data Structures

Before starting, keep in mind the following ideas:

Computers and humans need some structure in their language to communicate.
Different from humans, we should not allowed the computer to guess what we mean. Then, talking to the computer has to follow a particular set of rules so our orders are unambiguous.
Errors happen when we do not speak clearly to the computer; but it is worse if the computer does something we did not mean.
Data structures is the way the computer organizes pieces of data, so it can be stored, retrieved, used and modified.

We are going to talk about 3 data structures in R:

Lists.
Vectors.
Data Frame.

Lists and vectors are simple structures; a data frame is a more complex one (built from the simple ones).

List

Lists are containers of values. The values can be of any kind (numbers or non-numbers), and even other containers (simple or complex).

If we have an spreadsheet as a reference, a row is a ‘natural’ list.

Then this can be a list:

DetailStudent=list("Fred Meyers",
                   40,
                   FALSE)

The object DetailStudent serves to store temporarily the list in the computer. To name a list, use combinations of letters and numbers in a meaningful way (do not start with a number or a special character).

Typing the name of the object DetailStudent, now representing a list, will give you all the contents you saved in there:

DetailStudent

The list above has three elements. However, you may be wondering if those elements have a meaning altogether. In those situations, it is better to have names for each elements.

DetailStudent=list(fullName="Fred Meyers",
                   age=40,
                   female=FALSE)

# seeing the result
DetailStudent

This list has three elements, which we can also call fields. Each of these, in this case, holds a different data type:

FullName holds characters
age holds a number
female holds a logical (Boolean) value.

You can access any of those elements using these approaches:

# position
DetailStudent[[1]]

# name of the field
DetailStudent[['fullName']]

# name of the field
DetailStudent$fullName

If you do not have names for the list fields, you can only access them using positions:

NewList=list('a','b','c','d',1,2,3)
NewList[[1]]

Once you access an element, you can alter it:

DetailStudent[[1]]='Alfred Mayer'
# Then:
DetailStudent

You can even add an totally NEW field like this:

DetailStudent$city='Seattle'

# show:
DetailStudent

And destroy it by NULLing it, like this:

DetailStudent$city=NULL # do you like: DetailStudent[[4]]=NULL
DetailStudent

You can get rid of a list using:

rm(DetailStudent)
DetailStudent

** How would you create a list of this person out of his personal information data?**

Course: Data-Driven Management and Policy

Prof. José Manuel Magallanes, PhD

Session 3: Data Structures

List