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Identify coordinate columns in a data frame

Source: R/latlong_column.R
latlong_column.Rd

Detects latitude, longitude, and combined coordinate columns based on value ranges and format matching. Supports decimal degree, DMS (DDdeg MM'SS''}), and base-60 (\code{DDdeg MM') coordinate formats. Returns a named list with elements combined, latitude, and longitude, each containing the names and indices of detected columns.

Usage

latlong_column(data, sep = ",")

Arguments

data

A data frame to search for coordinate columns.

sep

Character. Separator used to split combined coordinate columns (i.e. columns containing both latitude and longitude as a single string). Default is ",".

Value

A named list with three elements:

combined

Columns containing both latitude and longitude as a single delimited string (e.g. "51.5,-0.1").

latitude

Columns containing latitude values only. Numeric range is constrained to [-90, 90].

longitude

Columns containing longitude values only. Numeric range is constrained to [-180, 180]. Columns already assigned to combined or latitude are excluded.

Each element is a named list mapping column name to column index in data. An empty named list (list()) is returned for any coordinate type not detected.

Details

Detection follows this priority order: combined columns are identified first, then latitude, then longitude. A column can only appear in one category — latitude candidates are excluded from longitude, and combined candidates are excluded from both.

The three recognised coordinate formats are:

  • Decimal degrees: "-12.345" or "51.5"

  • DMS: "12°34'56''N"

  • Base-60: "12°34'N"

Detection is based on value content, not column names, so columns with non-standard names (e.g. "point_y") will still be detected provided their values match a recognized coordinate format and pass the range check. At least one valid coordinate value is required for a column to be detected.

See also

latlong_format for checking the coordinate format of detected columns,

latlong_filter for removing invalid coordinates from detected columns.

st_as_sf for converting detected coordinate columns to an sf spatial object,

geocode for adding coordinates to a data frame from address strings.

Examples

df <- data.frame(
  id  = 1:6,
  lat = c(51.5, 48.8, 40.7, 35.6, -33.9, 55.8),
  lon = c(-0.1, 2.3, -74.0, 139.7, 151.2, 37.6)
)

# Detect separate latitude and longitude columns
latlong_column(df)
#> $combined
#> named list()
#> 
#> $latitude
#> $latitude$id
#> [1] 1
#> 
#> $latitude$lat
#> [1] 2
#> 
#> 
#> $longitude
#> $longitude$lon
#> [1] 3
#> 
#> 

# Access detected column names and indices
result <- latlong_column(df)
result$latitude
#> $id
#> [1] 1
#> 
#> $lat
#> [1] 2
#> 
result$longitude
#> $lon
#> [1] 3
#> 

# Detect a combined coordinate column
df2 <- data.frame(
  id     = 1:6,
  coords = c("51.5,-0.1", "48.8,2.3", "40.7,-74.0",
             "35.6,139.7", "-33.9,151.2", "55.8,37.6")
)
latlong_column(df2)
#> $combined
#> $combined$coords
#> [1] 2
#> 
#> 
#> $latitude
#> $latitude$id
#> [1] 1
#> 
#> 
#> $longitude
#> named list()
#> 

# Use a custom separator for combined columns
df3 <- data.frame(
  coords = c("51.5;-0.1", "48.8;2.3", "40.7;-74.0",
             "35.6;139.7", "-33.9;151.2", "55.8;37.6")
)
latlong_column(df3, sep = ";")
#> $combined
#> $combined$coords
#> [1] 1
#> 
#> 
#> $latitude
#> named list()
#> 
#> $longitude
#> named list()
#>