Making a presence absence dataset from only presences

pres_abs_creation.R

# load necessary packages
library(dplyr)
library(tidyr)

# create sample dataset
am_i_here <- data.frame(time_step = rep(1:5, each = 10)) %>%
  group_by(time_step) %>%
  mutate(individual = sample(letters, 10)) %>%
  ungroup()

# time steps and a bunch of "caught" individuals in that time step
am_i_here

# create master dataset
master <- am_i_here %>%
  expand(time_step, individual)

# add a column to am_i_here so that presence is defined
am_i_here$presence <- 1

new_master <- left_join(master, am_i_here)

# lots of NAs (absences)
filter(new_master, is.na(presence))

# make these NA
new_master$presence[is.na(new_master$presence)] <- 0

filter(new_master, is.na(presence))