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data-structures-R.md

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Data Structures
R

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]({{ site.baseurl }}/exercises/Vectors-shrub-volume-vectors-R/).

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

Projects

  • Problems with working directories
  • Turn folder into project
  • Creates .Rproj file
    • Isn’t project itself
    • Contains project info
    • Don’t change manually

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]({{ site.baseurl }}/data/shrub-dimensions-labeled.csv) 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]({{ site.baseurl }}/exercises/Data-frames-shrub-volume-data-frame-R).

Assign remaining exercises. Submit as compressed main folder, see [Assignment Submission & Checklist]({{ site.baseurl. }}/materials/turn-in-checklist)