r Counting occurences of specific number between specific number - r

Question

I have a matrix where each element is eather 0 or 1.
I would like to obtain the frequencies of consecutive occurences of 0's in each row, given the last 0 in the sequence is followed by a 1.
For example:
A row with: 0, 1 , 0, 1, 0, 0
The expected result should be:
Consecutive 0's of length: 1
Frequency : 2
Another row with: 0, 1, 0, 0, 1, 0, 0, 0, 1
The expected result:
Consecutive 0's of length: 1 2 3
Frequency: 1 1 1
A further objective is then to sum the frequencies of the same length in order to know how many times a single 0 was followed by a 1, two consecutive 0's where followed by a 1 etc.
Here is an exemplary matrix on which I would like to apply the routine:
m = matrix( c(1, 0, 1, 1, 1, 1, 0, 0, 0, 0,
1, 1, 1, 1, 0, 1, 0, 0, 0, 0,
1, 0, 0, 0, 1, 1, 1, 0, 0, 0,
0, 1, 0, 0, 0, 0, 0, 1, 1, 1,
1, 1, 1, 0, 0, 0, 0, 0, 1, 0,
1, 0, 0, 0, 0, 0, 1, 1, 0, 0),
ncol = 10, nrow = 6, byrow=TRUE)
The expected result should then be like the matrix below:
result = matrix( c(3, 0, 1, 0, 3, 0, 0, 0, 0, 0), ncol=10, nrow=1)
colnames(result) <- c("1", "2", "3", "4", "5", "6", "7", "8", "9", "10")
Where the column names are the lengths of consecutive 0's (followed by a 1) and the matrix entries the corresponding frequencies.
Note that I have a very large data matrix, and if possible I'd like to avoid loops. Thanks for any hints, comments and propositions.

Answer 1

Using base functions. The complication is you are discarding trailing zeros that do not end with 1.
Explanation in line.
set.seed(13L)
numRows <- 10e4
numCols <- 10
m <- matrix(sample(c(0L, 1L), numRows*numCols, replace=TRUE),
byrow=TRUE, ncol = numCols, nrow = numRows)
#add boundary conditions of all zeros and all ones
m <- rbind(rep(0L, numCols), rep(1L, numCols), m)
#head(m)
rStart <- Sys.time()
lens <- unlist(apply(m, 1, function(x) {
#find the position of the last 1 while handling boundary condition of all zeros
idx <- which(x==1)
endidx <- if (length(idx) == 0) length(x) else max(idx)
beginidx <- if(length(idx)==0) 1 else min(idx)
#tabulate the frequencies of running 0s.
runlen <- rle(x[beginidx:endidx])
list(table(runlen$lengths[runlen$values==0]))
}))
#tabulating results
res <- aggregate(lens, list(names(lens)), FUN=sum)
ans <- setNames(res$x[match(1:ncol(m), res$Group.1)], 1:ncol(m))
ans[is.na(ans)] <- 0
ans
# 1 2 3 4 5 6 7 8 9 10
#100108 43559 18593 7834 3177 1175 387 103 0 106
rEnd <- Sys.time()
print(paste0(round(rEnd - rStart, 2), attr(rEnd - rStart, "units")))
#[1] "27.67secs"
Do let me know the performance after running on the large matrix.