Basic question, how do I convert type character LINESTRING variable to a geometry type in sf and then separately, separate the two coordinates into different variables. E.g.
library(tidyverse)
library(sf)
df <- structure(list(geometry = c("LINESTRING (-85.76 38.34, -85.72 38.38)",
"LINESTRING (-85.46 38.76, -85.42 38.76)",
"LINESTRING (-85.89 38.31, -85.85 38.32)"
), var1 = c(4, 5, 6
), var2 = c(1, 2, 3
)), row.names = c(NA, -3L), class = c("tbl_df", "tbl", "data.frame"
))
df
# # A tibble: 3 x 3
# geometry var1 var2
# <chr> <dbl> <dbl>
# 1 LINESTRING (-85.76 38.34, -85.72 38.38) 4 1
# 2 LINESTRING (-85.46 38.76, -85.42 38.76) 5 2
# 3 LINESTRING (-85.89 38.31, -85.85 38.32) 6 3
Desired output:
final
# geometry start_lon start_lat end_lon end_lat var1 var2
# -85.76, -85.72, 38.34, 38.38 -85.76 38.34 -85.72 38.38 4 1
# -85.46, -85.42, 38.76, 38.76 -85.46 38.76 -85.42 38.76 5 2
# -85.89, -85.85, 38.31, 38.32 -85.89 38.31 -85.85 38.32 6 3
#so I can quickly plot lines between points
plot(final[, "var1"])
I thought some combination like final <- st_as_sf(df) %>% st_geometry(geometry) would convert it but I cant figure it out. Perhaps sfheaders is useful here?
EDIT
I want an sf type solution and not to manually extract coordinates.
Any suggestions? thanks
library(sf) can read Well-known Text direclty, if you tell it to using the wkt = argument. This gives you your sf object.
sf <- sf::st_as_sf( df, wkt = "geometry" )
sf
# Simple feature collection with 3 features and 2 fields
# geometry type: LINESTRING
# dimension: XY
# bbox: xmin: -85.89 ymin: 38.31 xmax: -85.42 ymax: 38.76
# CRS: NA
# geometry var1 var2
# 1 LINESTRING (-85.76 38.34, -... 4 1
# 2 LINESTRING (-85.46 38.76, -... 5 2
# 3 LINESTRING (-85.89 38.31, -... 6 3
Then there are many ways you can get the coordinates out and reshape them. Here I'm using sfheaders to convert the sf object to a long data.frame, then using library(data.table) to reshape it.
library(sfheaders)
library(data.table)
dt <- sfheaders::sf_to_df( sf, fill = TRUE )
setDT( dt )
## In this example, every 2nd row is to be made into new columns
odds <- 1:nrow(dt) %% 2 == 1
evens <- !odds
dt <- dt[odds][
dt[evens, .(end_lon = x, end_lat = y, linestring_id)]
, on = "linestring_id"
]
setnames( dt, c("x","y"), c("start_lon", "start_lat"))
dt
# var1 var2 sfg_id linestring_id start_lon start_lat end_lon end_lat
# 1: 4 1 1 1 -85.76 38.34 -85.72 38.38
# 2: 5 2 2 2 -85.46 38.76 -85.42 38.76
# 3: 6 3 3 3 -85.89 38.31 -85.85 38.32
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