[R] for loop not working

[Jim Lemon]

Hi mnw,
It looks to me as though you are testing the entire "holder" list each time
you go through the function. First, I'm not sure that a simple "==" is the
test you want. "movement" seems to be more than a single value and so you
might want to write a function that tests whether all of the components of
two "movement" objects are equal e.g.:

move_change<-function(currentx,previousx) {
 if(currentx$speed == previousx$speed) {
  if(currentx$heading == previousx$heading) return(0)
 }
 return(1)
}

Second, you probably don't want to test the entire list each time you loop
through the function. Just use:

 if(i > 1) changes<-move_change(movement,holder)
 holder<-movement

Jim


On Sat, Oct 10, 2015 at 2:08 AM, mnw <maw90 at aber.ac.uk> wrote:

> 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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> Sent from the R help mailing list archive at Nabble.com.
>
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