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 at gmail.com>
Sent: Thursday, June 9, 2022 4:39 PM
To: Howard, Tim G (DEC) <tim.howard at dec.ny.gov>
Cc: r-sig-geo at r-project.org <r-sig-geo at 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 at 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 at 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