R：将 function 应用于嵌套列表

Question

I have nested lists with numeric vales. In my case they are longitudes and latitudes sorted like this:

list1 <- list(1:50, 1:25, 1:30)
list2 <- list(1:50, 1:25)
list3 <- list(1:30)
list4 <- list(1:50, 1:25, 1:30, 1:45)
nested_lons1 <- list(list1, list2, list3, list4) 
nested_lons2 <- list(list1, list2, list3, list4) 
nested_lats1 <- list(list1, list2, list3, list4) 
nested_lats2 <- list(list1, list2, list3, list4)

Random numbers just for illustration purposes. I would like to calculate the distance between two points of each nested list (list1 until list4) using the Haversine formula. I read that it is better to avoid for loops which is why I'm looking at lapply.

dist <- lapply(1:4, function(x) distHaversine(c(nested_lons1[x],nested_lats1[x]),
                                              c(nested_lons2[x],nested_lats2[x]), r = 6371)) 

This gives an error like "can't be converted to double". I think the index is also wrong, since the function should iterate through the first list's nested lists, then go to the nested lists in the second list and so on until the 4th one. How can I do this? Any other (better) approach? Thank you!

Answer 1

If your list structures match, as they do in your example, it may be simpler to unlist and then relist the data. First unlist the lon/lat data and cbind to make 2-column matrices:

library(geosphere)
p1 <- cbind(unlist(nested_lons1), unlist(nested_lats1))
p2 <- cbind(unlist(nested_lons2), unlist(nested_lats2))

Now compute the distances and convert back to a list of the same structure:

d12 <- distHaversine(p1, p2)
d12.lst <- relist(d12, nested_lons1)
str(d12.lst)
# List of 4
#  $ :List of 3
#   ..$ : num [1:50] 0 0 0 0 0 0 0 0 0 0 ...
#   ..$ : num [1:25] 0 0 0 0 0 0 0 0 0 0 ...
#   ..$ : num [1:30] 0 0 0 0 0 0 0 0 0 0 ...
#  $ :List of 2
#   ..$ : num [1:50] 0 0 0 0 0 0 0 0 0 0 ...
#   ..$ : num [1:25] 0 0 0 0 0 0 0 0 0 0 ...
#  $ :List of 1
#   ..$ : num [1:30] 0 0 0 0 0 0 0 0 0 0 ...
#  $ :List of 4
#   ..$ : num [1:50] 0 0 0 0 0 0 0 0 0 0 ...
#   ..$ : num [1:25] 0 0 0 0 0 0 0 0 0 0 ...
#   ..$ : num [1:30] 0 0 0 0 0 0 0 0 0 0 ...
#   ..$ : num [1:45] 0 0 0 0 0 0 0 0 0 0 ...

Of course, this only works if the four nested lists have the same structure.