more user-friendly error msg in scatter_gplot()

Author: haotian127

src/helpers.jl

@@ -126,7 +126,7 @@ function scatter_gplot(X; marker = nothing, ms = 4, plotOrder = :normal, c = :vi
         if size(marker) == (N,) || size(marker) == (N, 1)
             marker = marker[:]  # reshape N x 1 matrix to a vector of length N
         else
-            error("marker only accepts a vector of length N or an N x 1 matrix, where N is the total number of points.")
+            error("marker only accepts a vector of length $(N) or an $(N) x 1 matrix.")
         end
         if plotOrder == :normal
             idx = 1:N
@@ -162,7 +162,7 @@ function scatter_gplot!(X; marker = nothing, ms = 4, plotOrder = :normal, c = :v
         if size(marker) == (N,) || size(marker) == (N, 1)
             marker = marker[:]  # reshape N x 1 matrix to a vector of length N
         else
-            error("marker only accepts a vector of length N or an N x 1 matrix, where N is the total number of points.")
+            error("marker only accepts a vector of length $(N) or an $(N) x 1 matrix.")
         end
         if plotOrder == :normal
             idx = 1:N