improve sampling

src/function.jl

 using Statistics: mean
-using StaticArrays: SA, SArray, MVector, MMatrix
+using StaticArrays: SA, SArray, MVector, MMatrix, SUnitRange
 using DataFrames, CSV
 export FeSpace, Mapper, FeFunction, ImageFunction, P1, DP0, DP1
 export interpolate!, sample, bind!, evaluate, integrate, nabla, save_csv
@@ -235,6 +235,7 @@ end
 Base.show(io::IO, ::MIME"text/plain", x::Derivative) =
     print("$(nameof(typeof(x))) of $(typeof(x.f))")
 
+# TODO: should be called "derivative"
 function nabla(f)
     d = ndims_domain(f.space.mesh)
     Derivative(f, zero(MMatrix{d, d, Float64}))
@@ -317,17 +318,22 @@ end
 bind!(f::FacetDivergence, cell) = f.cell[] = cell
 
 
-
 function sample(f::FeFunction)
+    out = _sample(f)
+    return f.space.size == (1,) ?
+        reshape(out, size(out)[2:end]) : out
+end
+
+function _sample(f::FeFunction)
     # assumes dual grid
     mesh = f.space.mesh
 
     m0 = NTuple{2}(minimum(mesh.vertices, dims = 2))
     m1 = NTuple{2}(maximum(mesh.vertices, dims = 2))
 
-    # TODO: make typesafe when introducing zero-dim space size ()
-    outsize = f.space.size == (1,) ?
-        round.(Int, m1 .- m0 .+ 1) : (f.space.size, round.(Int, m1 .- m0 .+ 1)...)
+    fcolon = ntuple(_ -> :, length(f.space.size))
+
+    outsize = (f.space.size..., round.(Int, m1 .- m0 .+ 1)...)
     out = similar(f.data, outsize)
     for cell in cells(mesh)
         bind!(f, cell)
@@ -341,9 +347,11 @@ function sample(f::FeFunction)
 
 	for I in CartesianIndex(I0[1], I0[2]):CartesianIndex(I1[1], I1[2])
             x = SVector(Tuple(I) .+ m0)
-            xloc = (A[:, 2:3] .- A[:, 1]) \ (x .- A[:, 1])
+            # TODO: move to global-to-local function or inside-triangle test
+            xloc = (A[:, SUnitRange(2, 3)] .- A[:, 1])::SArray \
+                (x .- A[:, 1])
 	    if all(xloc .>= 0) && sum(xloc) <= 1
-                out[I + CartesianIndex(1, 1)] = evaluate(f, xloc)[1]
+                out[fcolon..., I + CartesianIndex(1, 1)] .= evaluate(f, xloc)
             end
 	end
     end