[R-sig-Geo] df with embedded wkt lists to sf

[Josiah Parry]

Hey Tim,

The key thing here is to separate the long / lat points into elements in a
vector. You can do this with a string split. Afterwards, separate these
into their own rows like I've done below.

I think this should get you on the right path!


dat <- dget(textConnection(txtString))

dat |>
  tidyr::unnest(c(longitude, latitude)) |>
  dplyr::mutate(longitude = strsplit(longitude, "; "),
                latitude = strsplit(latitude, "; ")) |>
  tidyr::unnest(c(longitude, latitude)) |>
  sf::st_as_sf(coords = c(2, 3), crs = 4326)

On Thu, Jun 9, 2022 at 3:48 PM Howard, Tim G (DEC) via R-sig-Geo <
r-sig-geo using r-project.org> wrote:

> Howdy all -
> There's probably a way to do this much​ more simply than I've figured it
> out, so it's a bit embarrassing but here goes. I'm getting data out of a
> shiny app that looks like the following, with lists of coordinates within
> separate longitude and latitude columns.
>
> Is there more efficient way to get an `sf` collection than what I've got?
> Perhaps an `apply` replacement for the for() loop? Using a tibble because
> that's how `googlesheets4` gives it to me.
>
> # set up a couple of lines strings. lists within data.frame/tibble
> txtString <- 'structure(list(comment = c("line one", "line two"),
> longitude = list("-115.138577; -114.942454; -114.170219", "-118.411382;
> -118.153971; -117.83527; -117.246901; -117.026262; -117.185613"),
> latitude = list("37.527588; 38.234088; 38.368805", "41.296472; 41.645606;
> 41.819467; 41.837741; 41.590604; 41.333312")),
> row.names = c(NA, -2L), class = c("tbl_df", "tbl", "data.frame"))'
>
> dat <- dget(textConnection(txtString))
>
> # function for parsing the text strings
> getWKT <- function(x){
>   st_linestring(matrix(
>     c(as.numeric(unlist(strsplit(x$longitude[[1]],";"))),
>       as.numeric(unlist(strsplit(x$latitude[[1]],";")))),
>     byrow = FALSE, ncol = 2)
>   )
> }
>
> # populate dataframe/tibble by going back to sf text
> dat$wkt <- NA
> for(i in 1:nrow(dat)){
>   dat$wkt[[i]] <- st_as_text(getWKT(dat[i,]))
> }
>
> # finally make the sf collection
> dat_sf <- st_as_sf(dat, wkt = "wkt", crs = 4326)
>
>
> Thanks in advance for any tips.
> Tim
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