Get all sequences of contiguous values in a vector of integers.

`seqToIntervals(x)`

x

A vector of integers, for example, representing
indices. `x`

is coerced to integer, sorted, and unique values
extracted, if necessary, before finding the contiguous sequences.

A matrix with one row for each sequence, and two columns containing the start and the end of the sequence, respectively.

# NOT RUN { seqToIntervals(1:10) # [1 10] seqToIntervals(c(1:10, 15:18, 20)) # [1 10; 15 18; 20 20] # vectorised, so efficient for large vectors x seqToIntervals(sample(1:1000000, size=999990)) # }