CODEWITHSUNDEEP
rlistpoint
Александр Вьюн
Александр Вьюн

Reputation: 61

r list of objects POINT (coordinates)

I have a dataframe a.fil with Name, Lon and Lat. name1 43.37390 132.9703 name2 43.35311 132.7493 I create objects POINT

point1.sfg <- st_point(unname(unlist(a.fil[1, 2:3])))
point2.sfg <- st_point(unname(unlist(a.fil[2, 2:3])))

class(point1.sfg) [1] "XY" "POINT" "sfg"

I need to create list of objects POINT

ll <- list(point1.sfg, point2.sfg)

class(ll[[1]]) [1] "XY" "POINT" "sfg"

However, my dataframe contains 1000 rows If I use for...

i <- 1
for (i in 1:nrow(a.fil)) {
  ll[i] <- st_point(unname(unlist(a.fil[i, 2:3])))
}

I get list with nrow() elemets, but...

class(ll[[1]]) [1] "numeric"

How do I create list of objects POINT from this dataframe? non numeric

Help me!

Upvotes: 1

Views: 827

Answers (1)

SymbolixAU
SymbolixAU

Reputation: 26258

From a data.frame you can create an sf object

library(sf)

df <- data.frame(
    name = c("a","b","c")
    , lon = 1:3
    , lat = 3:1
)

sf <- sf::st_as_sf( df, coords = c("lon","lat" ) )
sf

# Simple feature collection with 3 features and 1 field
# geometry type:  POINT
# dimension:      XY
# bbox:           xmin: 1 ymin: 1 xmax: 3 ymax: 3
# CRS:            NA
#   name    geometry
# 1    a POINT (1 3)
# 2    b POINT (2 2)
# 3    c POINT (3 1)

Then the list of POINTs is just the geometry column

sf$geometry
# Geometry set for 3 features 
# geometry type:  POINT
# dimension:      XY
# bbox:           xmin: 1 ymin: 1 xmax: 3 ymax: 3
# CRS:            NA
# POINT (1 3)
# POINT (2 2)
# POINT (3 1)

str( sf$geometry )
# sfc_POINT of length 3; first list element:  'XY' num [1:2] 1 3

And if you truly want a list of POINT objects you can remove the sfc class

unclass( sf$geometry )
# [[1]]
# POINT (1 3)
# 
# [[2]]
# POINT (2 2)
# 
# [[3]]
# POINT (3 1)

Upvotes: 2

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