Использование geodist и ddply в R

Question

Я пытаюсь использовать функцию geodist в пакете gmt вместе с ddply в пакете plyr для вычисления расстояния между двумя наборами координат с помощью переменной группировки (Tow), но я получаю это сообщение:

Error: expecting result of length one, got : 8 
In addition: Warning messages: 
1: In N1 == N2 : 
    longer object length is not a multiple of shorter object length 
2: In E1 == E2 : 
    longer object length is not a multiple of shorter object length 

Набор данные организованы таким образом, что каждая строка имеет буксир, широту и долготу, и заказывает очесами и время. Я хотел бы рассчитать разницу в позиции между последовательными строками внутри буксировки.

Пример набора данных:

example <- structure(list(Tow = c(201602001L, 201602001L, 201602001L, 201602001L, 201602001L, 201602001L, 201602001L, 201602001L, 201602001L, 201602002L, 201602002L, 201602002L, 201602002L, 201602002L, 201602002L, 201602002L, 201602002L, 201602002L, 201602002L, 201602002L, 201602002L, 201602002L, 201602002L, 201602002L, 201602002L), Time = c("21:57:41", "21:58:30", "21:59:18", "22:00:06", "22:00:55", "22:07:14", "22:08:30", "22:09:46", "22:11:21", "23:10:40", "23:11:25", "23:12:11", "23:12:11", "23:12:55", "23:13:41", "23:14:27", "23:15:14", "23:16:00", "23:16:46", "23:17:32", "23:18:16", "23:19:02", "23:19:48", "23:20:34", "23:21:17"),  Long = c(-74.579651, -74.579631, -74.579754, -74.579885,  -74.580056, -74.579971, -74.580008, -74.580114, -74.580359,  -76.261671, -76.260058, -76.258475, -76.258475, -76.256906,  -76.255294, -76.253698, -76.252086, -76.25054, -76.248975,  -76.247434, -76.245858, -76.244288, -76.242696, -76.241143,  -76.239586), Lat = c(37.423733, 37.425438, 37.427116, 37.428796,  37.430466, 37.432135, 37.433818, 37.435483, 37.437141, 37.184116,  37.183005, 37.181895, 37.181895, 37.180741, 37.179638, 37.178505,  37.177406, 37.176231, 37.175095, 37.173918, 37.172818, 37.171664,  37.170543, 37.169419, 37.168305), Date = structure(c(2L,  2L, 2L, 2L, 2L, 2L, 2L, 2L, 2L, 1L, 1L, 1L, 1L, 1L, 1L, 1L,  1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L, 1L), .Label = c("2016/05/04",  "2016/05/05", "2016/05/06"), class = "factor"), TowStartDate = structure(c(1462334400,  1462334400, 1462334400, 1462334400, 1462334400, 1462334400,  1462334400, 1462334400, 1462334400, 1462334400, 1462334400,  1462334400, 1462334400, 1462334400, 1462334400, 1462334400,  1462334400, 1462334400, 1462334400, 1462334400, 1462334400,  1462334400, 1462334400, 1462334400, 1462334400), class = c("POSIXct",  "POSIXt"), tzone = ""), TowEndDate = structure(c(1462334400,  1462334400, 1462334400, 1462334400, 1462334400, 1462334400,  1462334400, 1462334400, 1462334400, 1462334400, 1462334400,  1462334400, 1462334400, 1462334400, 1462334400, 1462334400,  1462334400, 1462334400, 1462334400, 1462334400, 1462334400,  1462334400, 1462334400, 1462334400, 1462334400), class = c("POSIXct",  "POSIXt"), tzone = ""), InclinometerStart = c("21:57:40",  "21:57:40", "21:57:40", "21:57:40", "21:57:40", "21:57:40",  "21:57:40", "21:57:40", "21:57:40", "23:10:20", "23:10:20",  "23:10:20", "23:10:20", "23:10:20", "23:10:20", "23:10:20",  "23:10:20", "23:10:20", "23:10:20", "23:10:20", "23:10:20",  "23:10:20", "23:10:20", "23:10:20", "23:10:20"), InclinometerEnd = c("22:12:50",  "22:12:50", "22:12:50", "22:12:50", "22:12:50", "22:12:50",  "22:12:50", "22:12:50", "22:12:50", "23:26:10", "23:26:10",  "23:26:10", "23:26:10", "23:26:10", "23:26:10", "23:26:10",  "23:26:10", "23:26:10", "23:26:10", "23:26:10", "23:26:10",  "23:26:10", "23:26:10", "23:26:10", "23:26:10"), test = c(1,  1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,  1, 1, 1, 1, 1)), .Names = c("Tow", "Time", "Long", "Lat", "Date", "TowStartDate", "TowEndDate", "InclinometerStart", "InclinometerEnd", "test"), row.names = c(760L, 369L, 429L, 153L, 1467L, 949L, 1286L, 1080L, 1017L, 1893L, 3518L, 3041L, 3402L, 2803L, 2784L, 2897L, 3133L, 3000L, 3084L, 2723L, 3177L, 3572L, 2539L, 2768L, 2709L), class = "data.frame") 

Код:

library(plyr) 
library(gmt) 

new<-ddply(example, .(Tow), summarize, distance=geodist(tail(Lat-1), tail(Long-1),head(Lat,-1), head(Long,-1), units="km")) 

R информация:

R version 3.2.1 (2015-06-18) 
Platform: i386-w64-mingw32/i386 (32-bit) 
Running under: Windows 7 x64 (build 7601) Service Pack 1 

locale: 
[1] LC_COLLATE=English_United States.1252 
[2] LC_CTYPE=English_United States.1252 
[3] LC_MONETARY=English_United States.1252 
[4] LC_NUMERIC=C       
[5] LC_TIME=English_United States.1252  

attached base packages: 
[1] stats  graphics grDevices utils  datasets methods base  

other attached packages: 
[1] dplyr_0.4.3  plyr_1.8.3  gmt_1.2-0  RODBC_1.3-12 
[5] lubridate_1.5.0 rgdal_1.0-6  maptools_0.8-36 sp_1.1-1  

loaded via a namespace (and not attached): 
[1] Rcpp_0.11.6  lattice_0.20-31 assertthat_0.1 R6_2.1.0  
[5] grid_3.2.1  DBI_0.3.1  magrittr_1.5 stringi_0.5-5 
[9] lazyeval_0.1.10 tools_3.2.1  stringr_1.0.0 foreign_0.8-63 
[13] parallel_3.2.1 

Answer 1

В distance=geodist(tail(Lat-1), tail(Long-1),head(Lat,-1), head(Long,-1) ошибки относительно запятой.
С одной стороны вы пишете Lat, -1, а с другой стороны Lat-1.
Я думаю, что ваша ошибка исходит из этого.

J_F

Решение: Пример: такой же, как и выше, но не нужно пробельные очистку на вырезать и вставить)

library(plyr) 
library(gmt) 

## example as defined above 
new<-ddply(example, .(Tow), summarize, 
      distance=geodist(tail(Lat,-1), tail(Long,-1), 
      head(Lat,-1), head(Long,-1), units="km") 
     )