Loop will not execute in R - r

Question

I have a loop I want to execute that depends on the output of the previous loop in the code. This is the code;
holder <- list()
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 [[i]] <- (movement)
for (t in seq(1, length(holder))){
if (t == t-1)
changes <- 0
else if (t != t-1)
changes <- 1
}
You cannot see the beginning of loop but it results in a column of data called 'movements.'
I have attempted to temporarily store the 'movements' in the object 'holder.' What i want then is for the bottom for loop to go through 'holder' and label changes as either 0 or 1 in another column. Basically if the next 'movement' is not equal to the previous record the change as 0 and so forth. I think the problem is with the object 'holder' perhaps?
Currently I'm getting it to loop but it's only printing out a column of '1's.'
Any help much appreciated! Thanks.
Currently get the following output:
Movement Changes
left 1
right 1
forward 1
non-moving 1
non-moving 1
Think the problem lies in the list where movements are stored? Sorry, if I knew where the problem was I'd be more specific. Really new to this!
I end up with a data frame with column headers "Distance" "Speed" "Heading" "Movement" and "Changes." It's looping fine but for some reason Changes reults in a column of 1's as above. Is there an obvious mistake below?:
holder[[i]] <- (movement)
for (t in seq(1, length(holder))){
if (t == t-1)
changes <- 0
else if (t != t-1)
changes <- 1
I have also tried this, but then it doesn't loop at all.
holder[[i]] <- (movement)
for (t in seq(1, length(holder))){
if (holder[t] == holder[t-1])
changes <- 0
else if (holder[t] != holder[t-1])
changes <- 1
I'm currently getting this error: Error in holder[[t - 1]] : attempt to select less than one element
for the following code:
holder <- list(movement)
for (t in length(holder)){
if (holder[[t]] == holder[[t-1]])
changes <- 0
else changes <- 1

Answer 1

This is too long for a comment so I'm putting this as answer (actually it might answer your problem):
As I already mentioned in a comment to your previous question, you should have a look at what is seq(1, length(holder)) and so what you are doing when you put if (t == t-1) : you are doing something like "if 1==0" which cannot be TRUE.
You need to go with "the second version" of your loop (or, actually, without a loop...), which compares the right things, except that holder is a list so you need to either define it as a vector or use double brackets (holder[[t]]).
You don't need another if after else (what you are actually "saying" to R is "if A is true then do something, else, if 'opposite A' is true then do something else" but, necessarily, if A is not TRUE, then 'opposite A' is...
So something like:
for (t in seq(length(holder))){
if (holder[[t]] == holder[[t-1]]) changes <- 0 else changes <- 1
}
Please consider spending some time on the answer from your previous question to understand why your solution didn't work and why the answer provided did. (This includes reading documentations for the different functions and also take a look at the values your variable can take, e.g. running the loop, one "turn" at a time).