Joins

Remember to:

• display a fully joined version of the Portal data using:
  portal_bigtable <- inner_join(inner_join(surveys, species), plots)

Why use multiple tables

• Not efficient to include all information in a single table.
• Redundant information makes it more difficult to update or revise data.
  • Make changes in one place, not hundreds of places.
• Use multiple tables
• Each table contains a single kind of information
  • surveys: information about individuals
  • species: information about species
  • plots: information about plots
• If a species name changes we only need to change it in the species table
• Connect tables using joins to describe relationships between tables

Basic join

• Joins combine two tables using one or more columns
• inner_join keeps information from both tables that share a join field value

species <- read.csv("species.csv")
combined <- inner_join(surveys, species, by = "species_id")
head(combined)

• One way to think about this join is that it adds the information in species to the surveys table

Do Shrub Volume Join.

Multi-table join

• Use multiple joins to link multiple tables

portal_full <- inner_join(combined, plots, by = "plot_id")
head(portal_full)