cell_lines.r

# candidate answer to http://gis.stackexchange.com/questions/232044/how-to-identify-which-lines-polygons-intersect-when-using-raster-data-in-r

library(raster)
library(dplyr)
library(rgeos)
#####################
## Create toy data ##
#####################
df <- rbind(c(1,1), c(4,4),c(3,1), c(3,4))

coord_1 <- Line(rbind(c(1,1), c(4,4)))
coord_2 <- Line(rbind(c(3,1), c(3,4)))

l1 <- Lines(list(coord_1), ID = "road1")
l2 <- Lines(list(coord_2), ID = "road2")

Sl <- SpatialLines(list(l1, l2))

df <- data.frame(len = gLength(Sl, byid = TRUE))
#rownames(df) <- sapply(1:length(Sl), function(i) Sl@lines[[i]]@ID)

toy.lines <- SpatialLinesDataFrame(Sl, data = df, match.ID = FALSE)
toy.lines$polygon_id <- seq_len(nrow(toy.lines))
toy.lines$len = rgeos::gLength(toy.lines, byid  = TRUE)


## create the raster
r <- raster(extent(-0, 4, 0, 4), res = c(2, 2), crs = projection(toy.lines))
r[] <- seq_len(ncell(r))

library(tibble)
## I find this annoying having to tidy the list output, but it works fine
## note that if any line falls outside the raster, it will be NULL and would not
## work without this explicit handling
tabfun <- function(x)  {
  if (is.null(x)) {x <- integer(0L)}
  tibble(cell = x)
}
(cells <- bind_rows(lapply(cellFromLine(r, toy.lines), tabfun), .id = "line"))
## note that "line" is character integer of the position in toy.lines
## due to the .id collapse for bind_rows

## join for complete cases
cells %>% right_join(tibble(cell = seq_len(ncell(r))))