Index the walks by source and river size, for the exception test

knw_rule_in() tests a rule's exception by looking up, for each visit, the distance downstream to the first river of at least exc_q m³/s on one flow source. This turns knw_link_walks()'s long table into that lookup once, so a grid of thousands of rules does not re-filter it.

Usage

knw_walk_index(walks)

Arguments

walks

the table knw_link_walks() returns, with the target flags target_lake and target_regulated where the caller has them (absent columns read as FALSE).

Value

A named list, one element per src|qmin, each a list of pt (the start key "<blue_line_key> <downstream_route_measure>"), dist (Inf where the walk did not find a river), lake and reg.

Examples

w <- data.frame(blue_line_key = 1, downstream_route_measure = c(10, 10), src = "pick",
                qmin = c(3, 10), status = c("found", "none"), dist_m = c(400, NA))
names(knw_walk_index(w))
#> [1] "pick|10" "pick|3"