removing sequences of positive values between sequences of "0" - r

Question

I would like to create a small function in a data frame, for detecting (and setting to 0) sequences of positive values which are located between sequences of values equal to 0, but only if these sequences of positive values are not more than 5 values long.
Here's just a small example for showing you how my data looks (initial_data column), and what I would like to obtain at the end (final_data column):
DF<-data.frame(initial_data=c(0,0,0,0,100,2,85,0,0,0,0,0,0,3,455,24,10,7,6,15,42,0,0,0,0,0,0,0),final_data=c(0,0,0,0,0,0,0,0,0,0,0,0,0,3,455,24,10,7,6,15,42,0,0,0,0,0,0,0))
This sentence can also resume the trick:
"If there's a sequence of positive values, not longer than 5 values, and located between at least two or three 0-values (before and after this sequence of positive values), then set also this sequence to 0"
Any advice for doing this easily?
Thanks a lot!!!

Answer 1

Here's a possible approach using rle function :
DF<-data.frame(initial_data=c(0,0,0,0,100,2,85,0,0,0,0,0,0,3,455,24,10,7,6,15,42,0,0,0,0,0,0,0),
final_data=c(0,0,0,0,0,0,0,0,0,0,0,0,0,3,455,24,10,7,6,15,42,0,0,0,0,0,0,0))
# using rle create an object with the sequences of consecutive elements
# having the same sign (-1 means negative, 0 means zero, 1 means positive)
enc <- rle(sign(DF$initial_data))
# find the positive sequences having maximum 5 elements
posSequences <- which(enc$values == 1 & enc$lengths <= 5)
# remove index=1 or index=length(enc$values) if present because
# they can't be surrounded by 0
posSequences <- posSequences[posSequences != 1 &
posSequences != length(enc$values)]
# check if they're preceeded and followed by at least 2 zeros
# (if not remove the index)
toForceToZero <- sapply(posSequences,FUN=function(idx){
enc$values[idx-1]==0 &&
enc$lengths[idx-1] >= 2 &&
enc$values[idx+1] == 0 &&
enc$lengths[idx+1] >= 2})
posSequences <- posSequences[toForceToZero]
# reverse the run-length encoding, setting NA where we want to force to zero
v <- enc$values
v[posSequences] <- NA
# create the final data vector by forcing NAs to 0
final_data <- DF$initial_data
final_data[is.na(rep.int(v, enc$lengths))] <- 0
# check if is equal to your desired output
all(DF$final_data == final_data)
# > [1] TRUE

Answer 2

My best friend rle to the rescue:
notzero<-rle(as.logical(unlist(DF)))
Run Length Encoding
lengths: int [1:7] 4 3 6 8 20 8 7
values : logi [1:7] FALSE TRUE FALSE TRUE FALSE TRUE ...
Now just find all locations where values is TRUE and lengths < 5, and replace the values at those locations with FALSE . Then invoke inverse.rle to get the desired output.