Remember to

• Load surveys.csv data into surveys

• Aggregation combines rows into groups based on one of more columns.
• Calculates combined values for each group.
• First, group the data frame.

group_by(surveys, species_id)

• Different looking kind of data.frame
  • Source, grouping, and data type information

surveys_by_species <- group_by(surveys, species_id)

• Use summarize() to calculate values for each group.
• Count the number of rows for each group (individuals in each species).

summarize(surveys_by_species, abundance = n())

• Any function that returns a single value from a vector.
• E.g., mean.

species_weight <- summarize(surveys_by_species, avg_weight = mean(weight))

Null values

• mean(weight) when weight has missing values (NA)

• Returns NA

• Use filter() to remove the NAs

surveys_by_species <- filter(surveys_by_species, !is.na(weight))
species_weight <- summarize(surveys_by_species, avg_weight = mean(weight))

• na.omit() filters out rows with NA in any column

sp_weight_nonull <- na.omit(species_weight)

Do Shrub Volume Aggregation.