Using pixel_metrics() within a function does not work?

[zoeschindler]

Hello, I am not sure whether I found a bug, a feature or if I wrote bad code, but I have some code which is not working like I expected. I have an example here:

# load file
las <- readLAS(system.file("extdata", "Megaplot.laz", package="lidR"))

# set options
val <- 3

# get metrics without function
rast <- pixel_metrics(las, length(X) > val, res = 1)
# -> works

# get metrics with function
dummy <- function(las, minimum) {
  rast <- pixel_metrics(las, length(X) > minimum, res = 1)
}
dummy(las = las, minimum = val)
# -> does not work

When I use pixel_metrics inside a function, it does not work. I get an error that the variable "minimum" wasn't found. I get this traceback:

Fehler: Objekt 'minimum' nicht gefunden
10. `[.data.table`(las@data, , if (!anyNA(.BY)) length(X) > minimum, by = .(cells, echo)) at <text>#1
9. las@data[, if (!anyNA(.BY)) length(X) > minimum, by = .(cells, echo)] at <text>#1
8. eval(parse(text = cmd))
7. eval(parse(text = cmd))
6. metrics_classic(las, call, grp, filter)
5. template_metrics.LAS(las, func, template, ...)
4. template_metrics(las, func, template, ...)
3. pixel_metrics.LAS(las, length(X) > minimum, res = 1)
2. pixel_metrics(las, length(X) > minimum, res = 1)
1. dummy(las = las, minimum = val)

I am happy about any help!