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)

Do Bird Banding 1-4.

Working with multiple vectors

• Vector math combines values in the same position
• Element-wise: operating on one element at a time

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 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

• data.frame()

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

• read.csv()
  • Main argument is the location of the data - url or path on computer
  • Go to Datasets page on site and copy Shrub dimensions url

shrub_data <- read.csv('https://datacarpentry.org/semester-biology/data/shrub-dimensions-labeled.csv')

• 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”]]

Factors

str(shrub_data)

• The shrubID column has type Factor
• Special data type in R for categorical data
• Useful for statistics, but can mess up some aspects of computation
• Can eliminate during imports with stringsAsFactors

shrub_data <- read.csv('https://datacarpentry.org/semester-biology/data/shrub-dimensions-labeled.csv', stringsAsFactors = FALSE)
str(shrub_data)

Start Shrub Volume Data Frame, but just use the url instead of downloading the file.