Minimum travel cost to closest N number of opportunities — cost_to

Calculates the minimum travel cost to the closest N number of opportunities.

This function is generic over any kind of numeric travel cost, such as distance, time and money.

cost_to_closest(
  travel_matrix,
  land_use_data,
  opportunity,
  travel_cost,
  n = 1,
  group_by = character(0),
  active = TRUE,
  fill_missing_ids = TRUE
)

Arguments

travel_matrix: A data frame. The travel matrix describing the costs (i.e. travel time, distance, monetary cost, etc.) between the origins and destinations in the study area. Must contain the columns from_id, to_id and any others specified in travel_cost.
land_use_data: A data frame. The distribution of opportunities within the study area cells. Must contain the columns id and any others specified in opportunity.
opportunity: A string. The name of the column in land_use_data with the number of opportunities/resources/services to be considered when calculating accessibility levels.
travel_cost: A string. The name of the column in travel_matrix with the travel cost between origins and destinations.
n: A numeric vector. The minimum number of opportunities that should be considered. Defaults to 1. If more than one value is provided, the output includes an extra column specifying the number of opportunities that the minimum travel cost refers to.
group_by: A character vector. When not character(0) (the default), indicates the travel_matrix columns that should be used to group the accessibility estimates by. For example, if travel_matrix includes a departure time column, that specifies the departure time of each entry in the data frame, passing "departure_time" to this parameter results in accessibility estimates grouped by origin and by departure time.
active: A logical. Whether to calculate active accessibility (the of opportunities that can be reached from a given origin, the default) or passive accessibility (by how many people each destination can be reached).
fill_missing_ids: A logical. Calculating minimum travel cost to closest N number of opportunities may result in missing ids in the output if they cannot reach the specified amount of opportunities across all destinations they can reach. For example, estimating the minimum travel time that an origin that can only reach 4 opportunities takes to reach 5 opportunities resulting in such origin not being included in the output. When TRUE (the default), the function identifies which ids would be left out from the output and fill their respective minimum travel costs with Inf, which incurs in a performance penalty.

Value

A data frame containing the accessibility estimates for each origin/destination (depending if active is TRUE or FALSE) in the travel matrix.

Examples

data_dir <- system.file("extdata", package = "accessibility")
travel_matrix <- readRDS(file.path(data_dir, "travel_matrix.rds"))
land_use_data <- readRDS(file.path(data_dir, "land_use_data.rds"))

df <- cost_to_closest(
  travel_matrix,
  land_use_data,
  n = 1,
  opportunity = "schools",
  travel_cost = "travel_time"
)
head(df)
#> Key: <id>
#>                 id travel_time
#>             <char>       <num>
#> 1: 89a881a5a2bffff          29
#> 2: 89a881a5a2fffff          24
#> 3: 89a881a5a67ffff          28
#> 4: 89a881a5a6bffff          33
#> 5: 89a881a5a6fffff          32
#> 6: 89a881a5b03ffff          17

df <- cost_to_closest(
  travel_matrix,
  land_use_data,
  n = c(1, 2),
  opportunity = "schools",
  travel_cost = "travel_time"
)
head(df)
#> Key: <id, n>
#>                 id     n travel_time
#>             <char> <num>       <num>
#> 1: 89a881a5a2bffff     1          29
#> 2: 89a881a5a2bffff     2          32
#> 3: 89a881a5a2fffff     1          24
#> 4: 89a881a5a2fffff     2          25
#> 5: 89a881a5a67ffff     1          28
#> 6: 89a881a5a67ffff     2          31