work in progress to drop list item that is NULL

src/rmatio.c

@@ -1752,7 +1752,7 @@ write_elmt(const SEXP elmt,
     SEXP class_name;
 
     if (Rf_isNull(elmt))
-        return 1;
+        return 0;
 
     switch (TYPEOF(elmt)) {
     case CHARSXP:

tests/lists.R

@@ -0,0 +1,37 @@
+## rmatio, a R interface to the C library matio, MAT File I/O Library.
+## Copyright (C) 2013-2018  Stefan Widgren
+##
+## This program is free software: you can redistribute it and/or modify
+## it under the terms of the GNU General Public License as published by
+## the Free Software Foundation, either version 3 of the License, or
+## (at your option) any later version.
+##
+## rmatio is distributed in the hope that it will be useful,
+## but WITHOUT ANY WARRANTY; without even the implied warranty of
+## MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+## GNU General Public License for more details.
+##
+## You should have received a copy of the GNU General Public License
+## along with this program.  If not, see <http://www.gnu.org/licenses/>.
+
+library("rmatio")
+
+## For debugging
+sessionInfo()
+
+##
+## NULL: case-1
+##
+filename <- tempfile(fileext = ".mat")
+n1 <- list(x = 1, y = 2, z = NULL)
+write.mat(n1, filename = filename, compression = FALSE, version = c("MAT5"))
+stopifnot(identical(read.mat(filename), list(x = 1, y = 2)))
+unlink(filename)
+
+## Run the same test with compression
+if(rmatio:::have.zlib()) {
+    filename <- tempfile(fileext = ".mat")
+    write.mat(n1, filename = filename, compression = TRUE, version = c("MAT5"))
+    stopifnot(identical(read.mat(filename), list(x = 1, y = 2)))
+    unlink(filename)
+}