[R] for loop not working

[mnw]

Hi. I have some code which loops through raw GPS data. This initial loop
calculates distance, angle, speed etc between successive coordinates as well
as type of movement e.g.left, right, forward. I want to construct a second
loop that goes through the movements and records 'Changes' as either '0' or
'1' depending on whether the movement changed or not. I have put the whole
code in for reference but the additional loop begins at the object 'holder.'
I want to store movements in holder and then loop through holder to
determine 'changes.' At the moment it gives me 'Error in holder[[t - 1]] :
attempt to select less than one element.' The moment i make holder [[t]] it
works but just gives a list of '0's. I have tried many different things and
just cannot get it to work, so any help would be very much appreciated.
Again, sorry for the long post.




lst <- list() # temporary list to store the results
for (i in seq(1, nrow(R) - 1)){ # loop through each row of the 'R' matrix
  lat1 <- deg2rad(R[i, 4])
  long1 <- deg2rad(R[i, 5])
  lat2 <- deg2rad(R[i + 1, 4])
  long2 <- deg2rad(R[i + 1, 5])
  gcd_vif <- gcd.vif(lat1, long1, lat2, long2)
  
  # calc estimated speed by mean of speeds between two GPS records
  estSpeed <- (R[i, 6] + R[i+1, 6])/2
  
  # calculate acceleration (velocity)
  accel <- (R[i+1, 6] - R[i, 6]) / GPSSample
  
  # calculate absolute heading 
  heading <- absoluteHeading(lat1, long1, lat2, long2)

  # calculate bearing relative to previous GPS record
  relAngle <- 0
  # if the number of GPS records is less than 3 then no change in track
  if (i < 1) relAngle = heading
  # otherwise consider the previous heading in order to calculate the new
track
  else if (i > 0) {
    relAngle = (previousHeading - heading)
  
  }

  
  # determine whether movement is occurring and if so what type
  # if there are insufficient history items then just record movement types
discretely
   if (i < historyLength) movement <- movementType(relAngle, angleThreshold)
  
  else if (i > historyLength-1) {
    # Array to store speeds
    speedHistory <- array(historyLength)
    n = historyLength-1
    # get the speeds from the previous n (hisoryLength) "Movements" 
    for (j in seq(1, length(historyLength))){
      speedHistory [n] = R[i-j, 6]
      n-1
      }
      
      if (!bayesFilter(speedHistory, minSpeed, GPS_accy)) movement <-
"non-moving" 
      else if(bayesFilter(speedHistory, minSpeed, GPS_accy)) movement <-
movementType(relAngle, angleThreshold)
  
   
  }
  
  
  holder <- list(movement)
  holder [[i]] <- (movement)
  
  
  for (t in length(holder)){
    if (holder[[t]] == holder[[t-1]]) 
      changes <- 0
    else changes <- 1
    
  }
    
  
    
  # update previous heading information
  previousHeading = heading
 





  # Store the input data and the results
  lst[[i]] <- c(
    latitude_position_1 = lat1, 
    longtude_position_1 = long1, 
    latitude_position_2 = lat2, 
    longtude_position_2 = long2, 
    Distance = gcd_vif,
    Speed = estSpeed,
    Acceleration = accel,
    Absolute_Heading = heading,
    Relative_Heading = relAngle,
    Movement = movement,
    Changes = changes
  
  )
  
}  
Results <- as.data.frame(do.call(rbind, lst)) # store the input data and the
results in a data frame
Results



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