Updating 0 vector values based on preceding and successive values - r

Question

I have a data frame which has a cumulative count for each event (an event in this case being represented by a sequence of 1's in the bin column) with separating values given the value 0 and each event given an ID as such:
bin cumul ID
0 0 0
1 1 3
1 1 3
1 1 3
1 1 3
0 0 0
0 0 0
0 0 0
0 0 0
1 2 2
1 2 2
1 2 2
1 2 2
1 2 2
0 0 0
0 0 0
0 0 0
0 0 0
1 3 1
1 3 1
1 3 1
I want to update the ID column so each non-event (0 in the bin column) is assigned an ID value based on the previous and subsequent ID.
Therefore, if a non-event is preceded and succeeded by events of equal ID values (e.g. both 3) the non-event also carries this ID value (3). However if the non-event is preceded by an event with one value but succeeded with an event with a different value then the first half of the non-event is given an ID value equal to the preceding event and the final half of the non-event is given an ID value equal to the ID value of the succeeding event. Giving the final data frame:
bin cumul ID
0 0 3
1 1 3
1 1 3
1 1 3
1 1 3
0 0 3
0 0 3
0 0 2
0 0 2
1 2 2
1 2 2
1 2 2
1 2 2
1 2 2
0 0 2
0 0 2
0 0 1
0 0 1
1 3 1
1 3 1
1 3 1

Answer 1

If the question were how to fill in the zeros with ID that matched the preceding values, or matched successive values, then you could use na.locf from the zoo-package and it would be a one liner. For this task I think you might reach for the rle function:
rle(dat$ID)
#Run Length Encoding
# lengths: int [1:6] 1 4 4 5 4 3
# values : int [1:6] 0 3 0 2 0 1
Then thinking about how to use such result, my thinking was to use an algorithm like:
for each '0' in values; assign the first [`length`/2 + .9] values as $values[ idx-1 ]
assign the next ]`length`/2] values as $values[ idx+1 ]
( using `rep` will truncate/floor the fractional indices and adding a number
slightly less than 1.0 will take care of the edge cases where there are an
odd number of zeros in a row.)
( `sum` on the lengths can recover the correct positions.)
and for the beginning and ending 0-cases;
replace with successive and preceding values respectively
After considerable debugging effort (and commenting out the debugging cat-calls):
rldat <- rle(dat$ID)
for ( nth in seq_along( rldat$lengths) ){ #cat("nth=", nth, "\n")
if(rldat$values[nth] == 0){
if (nth == 1) { # cat("first value=",rldat$values[nth+1], "\n")
dat$ID[ 1:rldat$lengths[nth] ] <-rldat$values[nth+1];
} else {
if (nth== length(rldat$lengths) ){
dat$ID[ (length(dat$ID)-rldat$lengths[nth]+1):length(dat$ID) ] <-
rldat$values[nth-1]
} else {
# cat( "seq=", (sum(rldat$lengths[1:(nth- 1)])+1): sum(rldat$lengths[1:nth]) ,"\n")
dat$ID[ (sum(rldat$lengths[1:(nth-1)])+1):sum(rldat$lengths[1:nth]) ] <-
c( rep( rldat$values[nth-1],rldat$lengths[nth]/2+.9) ,
rep( rldat$values[nth+1],rldat$lengths[nth]/2) )}}
} }