How to index a vector sequence within a vector sequence

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And a recursive idea (edit on Feb 5 ’16 to work with NAs in pattern):

find_pat = function(pat, x) 
{
    ff = function(.pat, .x, acc = if(length(.pat)) seq_along(.x) else integer(0L)) {
        if(!length(.pat)) return(acc)

        if(is.na(.pat[[1L]])) 
            Recall(.pat[-1L], .x, acc[which(is.na(.x[acc]))] + 1L)
        else 
            Recall(.pat[-1L], .x, acc[which(.pat[[1L]] == .x[acc])] + 1L)
    }

    return(ff(pat, x) - length(pat))
}  

find_pat(1:2, myVector)
#[1] 3 7
find_pat(c(4, 1, 1), myVector)
#[1] 5
find_pat(1:3, myVector)
#integer(0)
find_pat(c(NA, 1), myVector)
#[1] 2
find_pat(c(3, NA), myVector)
#[1] 1

And on a benchmark:

all.equal(matchSequence(s, my_vec2), find_pat(s, my_vec2))
#[1] TRUE
microbenchmark::microbenchmark(matchSequence(s, my_vec2), 
                               flm(s, my_vec2), 
                               find_pat(s, my_vec2), 
                               unit = "relative")
#Unit: relative
#                      expr      min       lq   median       uq      max neval
# matchSequence(s, my_vec2) 2.970888 3.096573 3.068802 3.023167 12.41387   100
#           flm(s, my_vec2) 1.140777 1.173043 1.258394 1.280753 12.79848   100
#      find_pat(s, my_vec2) 1.000000 1.000000 1.000000 1.000000  1.00000   100

Using larger data:

set.seed(911); VEC = sample(c(NA, 1:3), 1e6, TRUE); PAT = c(3, 2, 2, 1, 3, 2, 2, 1, 1, 3)
all.equal(matchSequence(PAT, VEC), find_pat(PAT, VEC))
#[1] TRUE
microbenchmark::microbenchmark(matchSequence(PAT, VEC), 
                               flm(PAT, VEC), 
                               find_pat(PAT, VEC), 
                               unit = "relative", times = 20)
#Unit: relative
#                    expr       min       lq    median        uq       max neval
# matchSequence(PAT, VEC) 23.106862 20.54601 19.831344 18.677528 12.563634    20
#           flm(PAT, VEC)  2.810611  2.51955  2.963352  2.877195  1.728512    20
#      find_pat(PAT, VEC)  1.000000  1.00000  1.000000  1.000000  1.000000    20

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