Thursday, March 19, 2020 From rOpenSci (https://ropensci.org/blog/2020/03/19/parzer/). Except where otherwise noted, content on this site is licensed under the CC-BY license.
parzer is a new package for handling messy geographic coordinates. The first version is now on CRAN, with binaries coming soon hopefully (see note about installation below). The package recently completed rOpenSci review.
The idea for this package started with a tweet from Noam Ross (https://twitter.com/noamross/status/1070733367522590721) about 15 months ago.
The idea being that sometimes you have geographic coordinates in a messy format, or in many different formats, etc. You can think of it as being the package for geographic coordinates that lubridate is for dates.
I started off thinking about wrapping a Javascript library with Jeroen’s V8 R package, but then someone showed me or I found (can’t remember) some C++ code from back in 2006 that seemed appropriate. I figured I’d go down the C++ track instead of the Javascript track because I figured I could likely get better performance out of C++ and have slightly less install headaches for users.
The package is on CRAN so you can use install.packages
install.packages("parzer")
However, since this package requires compilation you probably want a binary. Binaries are not available on CRAN yet. You can install a binary like
install.packages("parzer", repos = "https://dev.ropensci.org/")
library(parzer)
Check out the package documentation to get started: https://docs.ropensci.org/parzer/
The following is a summary of the functions in the package and what they do:
Parse latitude or longitude separately
Parse latitudes and longitudes at the same time
Parse into separate parts of degrees, minutes, seconds
Pull out separately degrees, minutes, seconds, or hemisphere
Add/subtract degrees, minutes, seconds
Some examples:
parse latitudes and longitudes
lats <- c("40.123°", "40.123N74.123W", "191.89", 12, "N45 04.25764")
parse_lat(lats)
#> Warning in pz_parse_lat(lat): invalid characters, got: 40.123n74.123w
#> Warning in pz_parse_lat(lat): not within -90/90 range, got: 191.89
#> check that you did not invert lon and lat
#> [1] 40.12300 NaN NaN 12.00000 45.07096
longs <- c("45W54.2356", "181", 45, 45.234234, "-45.98739874N")
parse_lon(longs)
#> Warning in pz_parse_lon(lon): invalid characters, got: -45.98739874n
#> [1] -45.90393 181.00000 45.00000 45.23423 NaN
Sometimes you may want to parse a geographic coordinate into its component
parts; parse_parts_lat and parse_parts_lon are what you need:
x <- c("191.89", 12, "N45 04.25764")
parse_parts_lon(x)
#> Warning in pz_parse_parts_lon(scrub(str)): invalid characters, got: n45 04.25764
#> deg min sec
#> 1 191 53 23.99783
#> 2 12 0 0.00000
#> 3 NA NA NaN
pz_d(31)
#> 31
pz_d(31) + pz_m(44)
#> 31.73333
pz_d(31) - pz_m(44)
#> 30.26667
pz_d(31) + pz_m(44) + pz_s(59)
#> 31.74972
pz_d(-121) + pz_m(1) + pz_s(33)
#> -120.9742
Check out the parzer use cases vignette on the docs site. Get in touch if you have a use case that might be good to add to that vignette.
Thanks to the reviewers Maria Munafó and Julien Brun for their time invested in improving the package.
There’s more to do. We are thinking about dropping the Rcpp dependency, support parsing strings that have both latitude and longitude together, making error messages better, and more.
