Vectors

• A sequence of values with the same type
• Create using c(), which stands for “combine”

sites <- c("a", "a", "b", "b")

• Functions:
  • str(sites)
  • length(sites)
• Slicing:
  • sites[1]
  • sites[1:3]
    • 1:3 makes a vector. So, this is the same as
  • sites[c(1, 2, 3)]
    • You can use a vector to get any subset or order you want
• Math functions:

density_ha <- c(2.8, 3.2, 1.5, 3.8)
mean(density_ha)
max(density_ha)
min(density_ha)
sum(density_ha)

• Vector math combines values in the same position

density_ha <- c(2.8, 3.2, 1.5, 3.8)
area_ha <- c(3, 5, 1.9, 2.7)
total_number <- density_ha * area_ha

• Subsetting:
  • total_number[sites == 'a']
    • == means “equal to” in most languages.
    • Not =. = is used for assignment.
    • !=, <, >

Do Exercise 9 - Shrub Volume Vectors.

Matrices (if linear algebra folks)

• A two-dimensional set of values with a single data type

x <- matrix(1:6, 2)
y <- matrix(1:3, ncol = 1)
x %*% y

Data frames

• A list of equal length vectors grouped together
• Assignment:
  • data.frame()
  • read.csv()

surveys <- data.frame(sites, density_ha, area_ha)

• Useful commands:
  • str(surveys)
  • length(surveys)
  • nrow(surveys), ncol(surveys)
• Subsetting columns:
  • surveys["sites"]
  • surveys[c("counts", "weights")]
  • surveys$sites
  • surveys[["sites"]]

Importing data

• read.csv()
• Download the file for the Shrub Volume Data Frame exercise
• How do we tell R where this file is

When someone says setwd discuss issues

• Code doesn’t work on different computers
• Even worse if collaborating with several people Ask if anyone has heard of projects

Projects

• Start a new project
• Create a data subdirectory
• Download Shrub Volume Data Frame file to that directory
• Load it

shrub_data <- read.csv('./data/shrub-dimensions-labeled.csv')

DO NOT USE setwd() FOR THIS CLASS

Do Exercise 10 - Shrub Volume Data Frame.

Project structure

• Two common structures
• code in top-level directory with subdirectories for data, results, etc (possibly with subdirectories of their own)
• code in a separate subdirectory

Assign remaining exercises.