[R-sig-Geo] help: Problem getting centroids inside lists

[MacQueen, Don]

If all of your data frames had enough points then this should work:

myfun1 <- function(le) {
  list(one=geosphere::centroid(coordinates(le$one)),
       two=geosphere::centroid(coordinates(le$two))
       )
}

lapply(ct, myfun1)

To handle the one point case, try the following, which I think works with your example data, but is untested if there just two points.
It also assumes the data frames are named 'one' and 'two', and will ignore any others. To handle other names, I think you
could replace  $one  with  [[1]]  and  $two  with  [[2]]  .

myfun <- function(le) {
  list(one=if (length(le$one)>1) geosphere::centroid(coordinates(le$one)) else coodinates(le$one),
       two=if (length(le$two)>1) geosphere::centroid(coordinates(le$two)) else coordinates(le$two)
       )
}

lapply(ct, myfun)


To see a little bit of what's going on, try

  myfun(ct[[1]])
  myfun1(ct[[1]])
  myfun1(ct[[2]])
  myfun(ct[[2]])



I would also verify that the length method for objects of class SpatialPoints does return the number of points, as it appears to:

> class(ct$a$two)
[1] "SpatialPoints"
attr(,"package")
[1] "sp"

> length(ct$a$one)
[1] 3
> length(ct$a$two)
[1] 3
> length(ct$a$two)
[1] 3
> length(ct$b$two)
[1] 1

--
Don MacQueen
Lawrence Livermore National Laboratory
7000 East Ave., L-627
Livermore, CA 94550
925-423-1062
Lab cell 925-724-7509
 
 

On 9/10/18, 10:56 AM, "R-sig-Geo on behalf of Ariel Fuentesdi" <r-sig-geo-bounces using r-project.org on behalf of ariel.fuentesdi using usach.cl> wrote:

    Hi everyone,
    
    I have a list of coordinates called "ct" and I want to extract the
    centroids of each sublist, but it only works when it has only 3 or more
    points. In ct$b$two only has one point; in that case, I would rescue that
    point as If it were a centroid.
    
    This is what I did:
    
    library(dplyr)
    library(geosphere)
    
    ct <- list(a = list(one = data.frame(lon = c(-180, -160, -60), lat = c(-20,
    5, 0)),
                        two = data.frame(lon = c(-18, -16, -6), lat = c(-2, 50,
    10))),
               b = list(one = data.frame(lon = c(-9, -8, -3), lat = c(-1, 25,
    5)),
                        two = data.frame(lon = c(-90), lat = c(-1))))
    
    coordinates(ct$a$one) <- ~lon+lat
    coordinates(ct$a$two) <- ~lon+lat
    coordinates(ct$b$one) <- ~lon+lat
    coordinates(ct$b$two) <- ~lon+lat
    
    s <- 1:length(ct)
    ctply <- list()
    for (i in s){
     for (j in 1:length(ct[[i]])) {
      ctply[[i]][j] <- ifelse(test = lengths(ct[[i]][1]) > 2, yes = sapply(X =
    ct[[i]][j],
        FUN = function(y) geosphere::centroid(slot(y, "coords"))), no =
    ct[[i]][j] )
     }
    }
    
    Thanks in advance
    
    Regards,
    Ariel
    
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