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

[Josiah Parry]

Yeah, of course. I wouldn’t necessarily call it “convoluted!” It’s a pretty
standard data cleaning flow.

As a note, I was last and specified the coordinate columns by position. You
should provide a vector of the column names eg c(“x”, “y”). Check out the
help documentation for that function. It should be useful!

The process, if it’s not necessarily clear, separates each point to a row,
those points then are combined to multipoint and then cast as a line
string.

On Fri, Jun 10, 2022 at 07:16 Howard, Tim G (DEC) <tim.howard using dec.ny.gov>
wrote:

> Josiah,
> Interesting, thanks for working out and posting this approach. It may be
> just as complex and convoluted as what I've come up with! Dis-associating
> the line strings to points and then re-aggregating them to lines using
> group-by seems iffy to me, but it works (and for polygons as well).
>
> Of course I've got a much larger attribute table than just a "comments"
> column so the spot where you define 'coords=c(2,3)' doesn't work. But I've
> come up with a work-around to that by finding the location of the lon/lat
> columns before starting. And the attribute table is lost so it needs to be
> joined back in a step not needed in my approach.
>
> I guess this confirms that there isn't already a part of  st_as_sf​ I was
> missing!
> Thanks again,
> Tim
>
>
> From: Josiah Parry <josiah.parry using gmail.com>
> Sent: Thursday, June 9, 2022 4:39 PM
> To: Howard, Tim G (DEC) <tim.howard using dec.ny.gov>
> Cc: r-sig-geo using r-project.org <r-sig-geo using r-project.org>
> Subject: Re: [R-sig-Geo] df with embedded wkt lists to sf
>
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>
> Furthermore, if you want to get these points into a linstring you can
> combine the points by group (comment) and then cast them to a line like so
> below.
>
> This is an interesting use case! Thanks for introducing me to it.
>
> dat_sf |>
>   dplyr::group_by(comment) |>
>   dplyr::summarise(geometry = sf::st_cast(
>     sf::st_combine(geometry), "LINESTRING"
>     ))
>
> On Thu, Jun 9, 2022 at 4:34 PM Josiah Parry <josiah.parry using gmail.com>
> wrote:
> 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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