Cumulative sums over run lengths. Can this loop be vectorized?

Question

I have a data frame on which I calculate a run length encoding for a specific column. The values of the column, dir, are either -1, 0, or 1.

dir.r

Answer 1

Both Spacedman & Chase make the key point that a grouping variable simplifies everything (and Chase lays out two nice ways to proceed from there).

I'll just throw in an alternative approach to forming that grouping variable. It doesn't use rle and, at least to me, feels more intuitive. Basically, at each point where diff() detects a change in value, the cumsum that will form your grouping variable is incremented by one:

df$group <- c(0, cumsum(!(diff(df$dir)==0)))

# Or, equivalently
df$group <- c(0, cumsum(as.logical(diff(df$dir))))