Vectors

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

sites <- c("a", "a", "b", “c”)

• 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)]
  • sites[c(4, 1, 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 8 - Shrub Volume Vectors.

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[“area_ha”]
  • surveys[c(“area_ha”, “sites”)]
  • surveys$area_ha
  • surveys[[“area_ha”]]

Importing data

• read.csv()
• Download the file for the Shrub Volume Data Frame exercise
• Move to new data subfolder
• Load it

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

File paths

• Use relative path with projects
• Project is self-contained unit
• DO NOT USE setwd() FOR THIS CLASS
  • Code doesn’t work on different computers
  • Even worse if collaborating with several people

Do Exercise 9 - Shrub Volume Data Frame.