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Data Structures

Overview

  • Vector
    • Series of multiple values of the same type in one dimension
  • List
    • Series of multiple values of different types in one dimension
    • Lists can be nested within one another
  • Matrix
    • Rectangular array of the same data type
    • If the values are numbers, you can perform mathematical operations on each value
  • Data Frame
    • Data created by combining multiple vectors so that each vector becomes a column
    • Each column can have a different data type

Vectors

  • Vectors are the most basic element in R
  • All other elements are made up of vectors

Matrices

Creating a Matrix

  • Create a vector:
  • Turn the vector into a matrix:
  • Optionally, you can add row and column labels:

Setting Matrix Dimensions

  • The number of data points and the number of rows/columns determines the dimensions
    • In the code above, nrow = 3 is specified
    • Since there are only 6 data points, this by default means that there can only be 2 columns
  • If we had specified ncol = 3 in the same code, there would be only 2 rows by default

byrow Option

  • The default for matrix() is byrow = FALSE the first column will be filled, then the second column will be filled, etc. as shown above
  • If byrow = TRUE the first row will be filled, then the second row will be filled, etc.
    • The same matrix with byrow=TRUE specified is shown below

Matrices and Mathematical Operations

  • When a matrix is all numeric, you can perform mathematical operations with all values
  • If we want to purchase three of each fruit and want the total price, we can multiply each value by 3

Data Frames

  • A data frame is similar to a matrix except each column can be of a different type
  • Data frames are typically like data sets you would see in an Excel sheet
  • Every column is a variable
  • Remember: User $ to refer to a specific variable/column within a data frame
    • Example: rainfall.df$city

Using matrix() to Create a Data Frame

  • Can use the matrix() and data.frame() functions to create a data frame
    • First, create a matrix with your desired format
    • Then put this code into the data.frame() function

Lists

Simple Lists

  • Create a list with the list() function
  • Remember:
    • Lists can have multiple data types
    • Lists can be nested, meaning one list can be placed inside another list
  • Below is a simple example of a list:

Nested Lists

  • Below shows how to create a nested list (a list within a list):