Unexpected behavior in as.contour

[jmsigner]

Background

While migrating from raster to terra I found an unexpected behavior in the function as.contour() if the resulting SpatVect was only one single feature. Changing sapply() to lapply() on line 103 solved it:

terra/R/plot.R

Line 103 in c133566

y <- sapply(1:length(z), function(i) cbind(z[[i]]$level, i, z[[i]]$x, z[[i]]$y))

Example

as.contour_asis <- function(x, maxcells=100000, ...) {
            x <- spatSample(x[[1]], size=maxcells, method="regular", as.raster=TRUE)
            z <- grDevices::contourLines(x=xFromCol(x,1:ncol(x)), y=yFromRow(x, nrow(x):1), z=t(as.matrix(x, wide=TRUE)[nrow(x):1,]), ...)
            y <- sapply(1:length(z), function(i) cbind(z[[i]]$level, i, z[[i]]$x, z[[i]]$y))
            y <- do.call(rbind, y)
            y[] <- as.numeric(y)
            u <- unique(y[,1])
            y[,1] <- match(y[,1], u)
            colnames(y)[3:4] <- c("x", "y")
            vect(y, "lines", atts=data.frame(level=u), crs=crs(x))
}

as.contour_fixed <- function(x, maxcells=100000, ...) {
            x <- spatSample(x[[1]], size=maxcells, method="regular", as.raster=TRUE)
            z <- grDevices::contourLines(x=xFromCol(x,1:ncol(x)), y=yFromRow(x, nrow(x):1), z=t(as.matrix(x, wide=TRUE)[nrow(x):1,]), ...)
            y <- lapply(1:length(z), function(i) cbind(z[[i]]$level, i, z[[i]]$x, z[[i]]$y)) # changed to lapply here
            y <- do.call(rbind, y)
            y[] <- as.numeric(y)
            u <- unique(y[,1])
            y[,1] <- match(y[,1], u)
            colnames(y)[3:4] <- c("x", "y")
            vect(y, "lines", atts=data.frame(level=u), crs=crs(x))
}


# Creating a dummy data set
xy <- expand.grid(x = seq(-10, 10, 0.1), 
                  y = seq(-10, 10, 0.1))
xy$z <- pexp(0.75, sqrt(xy$x^2 + xy$y^2))
r <- rast(xy)

as.contour_asis(r, levels = c(0.4, 0.5))  # works as expected
as.contour_asis(r, levels = c(0.4))  # error

as.contour_fixed(r, levels = c(0.4, 0.5)) # works as expected
as.contour_fixed(r, levels = c(0.4)) # works as expected

[rhijmans]

Thanks!