Problems creating a new list - r

Question

Here I have a function which I want to equalize the number of stops from a object in motion. To carry out this, there is a position list (in which this function is named Trip), and duration which is the length of trip but will be used in further development of the code.
Now to know the number of the stop throughout the trip what I have to do is for each Trip, which has different positions as:
x,y,z
10,11,13
12,11,14
13,11,15,
....
**20,11,35
20,11,35
20,11,35**
Compare themselves to know which are equal.
On this last positions as the object remain on the same location we can conclude was stopped. So, in order to know the stop we need to compare each position with the next ones.
I write this code:
StopsNumber <- function(Trip,Duration)
{
i=1
aux = Trip
while(i<length(Trip))
{
if(aux[i] == aux[i+1] && aux[i] == aux[i+2]){
Stop = aux[i]
NStops = Nstops+1
}
aux = [aux+1]
i=i+1
} # end
return (Stop,Nstops)
}
MThe problem I think is that i do not know how to create list of things. For instance: on Stop = aux[i] I don't know if it is working out properly. Because i want to do Stop be a list (or a vector, with aux, (those positions where the object has been quiet).And doing this if there are more than one stops, the last one will replace the rest.
May somebody help me?
Thank you

Answer 1

Your definitions of movement, intervals and stops are unclear. Therefore the code is fairly long to avoid misunderstandings. Otherwise it could be boiled down one or two lines. First some clear cut definitions
An interval is some time between between to xyz-points
Movement has occured in an interval, if start and end point differ in space
A stop is an interval of no movement after an interval of movement
You can choose to assume the object was(or was not) in movement before the first interval. Thus a stop can happen already in first interval.
a tip: try out the loop-functions apply(), sapply(), lapply() and foreach() instead of the low-level for() and while().
the code
#your data added some more positions
mixed.vector = c(
10,11,13,
12,11,14,
13,11,15,
20,11,35,
20,11,35, #this is a stop
20,11,35,
13,11,25,
10,20,30,
10,20,30) #this is a stop
#convert data to appropiate data structure.
#I suggest a matrix. List of vector would also do
#some tricks to convert (multiple ways to do this)
#mixed vector to matrix
xyz.matrix = matrix(mixed.vector,ncol=3,byrow=TRUE)
print(xyz.matrix) #each row is a position, columns are x, y and z respectively.
#matrix to list of vectors (if this structure is preferred)
list_of_vectors = split(xyz.matrix,1:dim(xyz.matrix)[1])
print(list_of_vectors)
#list of vectors to matrix (if this is how your data initially is ordered)
xyz.matrix = do.call(rbind,list_of_vectors)
print(xyz.matrix) #and we're back with a matrix
#function checking if intervals have no movement
#(total number of intervals is number of positions minus 1)
find_interval_with_movement = function(XYZ.m) {
nrows = dim(XYZ.m)[1] #scalar of n.position rows
interval_with_movement = !apply(XYZ.m[-nrows,]==XYZ.m[-1,],1,all) #check pairs of row if x y z match.
return(interval_with_movement)
}
#function finding stops, optional assuming the object was moving before first interval
find_stops = function(interval_movements,object.moving.at.t0=TRUE) {
intervals_to_search= c(object.moving.at.t0,interval_movements)
len = length(intervals_to_search)
#search for intervals with no movement where previous interval has movement
did.stop = sapply(2:len,function(i) all(intervals_to_search[(i-1):i] == c(T,F)))
return(did.stop)
}
#these intervals has no movement
print(!find_interval_with_movement(xyz.matrix))
#these intervals had no movement, where previous had
print(find_stops(find_interval_with_movement(xyz.matrix)))
#and the full number of stops
print(sum(find_stops(find_interval_with_movement(xyz.matrix))))