Throw debug messages when substitution aren't possible when all value…

…s are missing.

src/imputors/substitute.jl

@@ -37,8 +37,18 @@ Substitute(; statistic=defaultstats) = Substitute(statistic)
 
 function _impute!(data::AbstractArray{Union{T, Missing}}, imp::Substitute) where T
     mask = .!ismissing.(data)
-    x = imp.statistic(disallowmissing(data[mask]))
-    return Base.replace!(data, missing => x)
+    # Since most summary statistics will require some data, we throw a debug message when
+    # all supplied values are missing
+    if any(mask)
+        x = imp.statistic(disallowmissing(data[mask]))
+        return Base.replace!(data, missing => x)
+    else
+        @debug(
+            "Cannot apply substitution function ($(imp.statistic)) " *
+            "when all values are missing"
+        )
+        return data
+    end
 end
 
 
@@ -82,8 +92,19 @@ end
 
 function _impute!(data::AbstractArray{Union{T, Missing}}, imp::WeightedSubstitute) where T
     mask = .!ismissing.(data)
-    x = imp.statistic(disallowmissing(data[mask]), imp.weights[mask])
-    return Base.replace!(data, missing => x)
+
+    # Since most summary statistics will require some data, we throw a debug message when
+    # all supplied values are missing
+    if any(mask)
+        x = imp.statistic(disallowmissing(data[mask]), imp.weights[mask])
+        return Base.replace!(data, missing => x)
+    else
+        @debug(
+            "Cannot apply weighted substitution function ($(imp.statistic)) " *
+            "when all values are missing"
+        )
+        return data
+    end
 end
 
 # Auxiliary functions defining our default substitution rules

test/imputors/substitute.jl

@@ -102,6 +102,12 @@
         )
         @test result == expected
     end
+
+    @testset "all missing" begin
+        a = [missing 2; missing 3]
+        # Test that substitution along columns with all missing data will just return that data.
+        Impute.substitute(a; dims=2) == a
+    end
 end
 
 @testset "WeightedSubstitute" begin
@@ -220,4 +226,10 @@ end
         )
         @test result == expected
     end
+
+    @testset "all missing" begin
+        a = [missing 2; missing 3]
+        # Test that substitution along columns with all missing data will just return that data.
+        Impute.wsubstitute(a; weights=eweights(2, 0.3), dims=2) == a
+    end
 end