Sf: create lat lon numeric columns from st_point feature /

[lucasmation]

in a sf object with ast_point column, how can one create additional numeric columns latand lon?

demo(nc, ask = FALSE, echo = FALSE)
nc <- st_centroid(nc)

nc$lat <- .... 
nc$lon <- .... 

EDIT: obs: I belive in Postgis it would be something like st_x and st_y

EDIT2: changed data.frame for sf as it seemed to be causing confusion

[edzer]

data.frames can't have an st_point column; otherwise they work as data.frames. This is not an sf related issue; pls read into how R works.

[lucasmation]

I understand how R works...

Are you referring to the fact that I used the word data.frame instead of sf? Anyway, I edited the original post with sf (edit2).

Flowing sf vignette1 I thought you could use either word interchangeably:

"As attributes are typically stored in data.frame objects (or the very similar tbl_df), we will also store feature geometries in a data.frame column.

sf, the table (data.frame) with feature attributes and feature geometries, which contains"

in any case, how to add numeric coluns lat and lon to a sf object?

[karldw]

Hey @lucasmation, here's a function I wrote a while back that will probably accomplish what you want.

library(sf)
library(dplyr)

geometry_to_lonlat <- function(x) {
  if (any(sf::st_geometry_type(x) != "POINT")) {
    stop("Selecting non-points isn't implemented.")
  }
  coord_df <- sf::st_transform(x, sf::st_crs("+proj=longlat +datum=WGS84")) %>%
    sf::st_coordinates() %>%
    dplyr::as_tibble() %>%
    dplyr::select(X, Y) %>%
    dplyr::rename(lon = X, lat = Y)
  out <- sf::st_set_geometry(x, NULL) %>%
    dplyr::bind_cols(coord_df)
  return(out)
}

In general, I've found it easier to get answers on stackoverflow than github. There's a whole #sf tag!

[lucasmation]

@karldw tks. This works!
(for a general function, I don't think the reprojection should be included.
This seems more natural:
x %>% st_transform( sf::st_crs("+proj=longlat +datum=WGS84")) %>% geometry_to_lonlat
)

tks

[edzer]

Sorry for my blunt earlier reply; I clearly misunderstood your question.

[lucasmation]

@edzer , no worries. I think adding functions st_x and st_y to sf wuold be nice

[Nowosad]

@lucasmation also take a look at https://github.com/r-spatial/sf/issues/284

[edzer]

> nc = st_centroid(nc)
> st_x = function(x) st_coordinates(x)[,1]
> st_x(nc)[1:3]
        1         2         3 
-81.49823 -81.12513 -80.68573 

IMO, functions that trivial clobber the namespace.