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+====== Save and load data in polymake ======
+In polymake there are different ways to save and load data depending on the type and the format of the data. We distinguish between `big' objects (Polytope, Matroid,...), complex data types (Set, Matrix, Array<Vector<html><Rational></html>>,...), and data from files in arbitrary formats.
+===== Handling polymake objects =====
+Let us take this nice example object:
+<code perl>
+> $p = cube(3);
+</code>
+To store big objects use the command
+<code perl>
+> save($p,"myPolyObject.poly");
+</code>
+This will create a file in JSON format. An existing files will be silently overwritten.
+To load a big object from such a file use the command
+<code perl>
+> $p=load("myPolyObject.poly");
+</code>
+If you did not start ''%%polymake%%'' in the directory containing your object, it is necessary to add the relative or absolute path, e.g.
+<code perl>
+$p=load("MyFolder/myPolyObject.poly");
+</code>
+TAB completion like in a usual UNIX shell supports you in navigating through the file system.
+**Note:** If you load a polymake object and compute new properties, these properties will automatically be added to the original file at the end of the session. You can suppress this with the command
+<code perl>
+> $p->dont_save;
+</code>
+called prior to leaving the session (but after the last computation with $p).
+If you want to store a collection of objects into a single file, there is an [[tarballs|extra tutorial]] for you.
+===== Handling complex data types =====
+Apart from big objects, you can also persistently store arbitrary data structures like matrices or graphs format via ''%%save_data%%'', e.g.
+<code perl>
+> $s=new Set<Int>(1,2,3,4);
+> save_data($s, "mySet.poly");
+</code>
+To load data objects from such a file use the command
+<code perl>
+> $s=load_data("mySet.poly");
+</code>
+In fact, the command pairs ''%%load%%''/''%%save%%'' and ''%%load_data%%''/''%%save_data%%'' are almost equivalent. The only difference is in filename handling: ''%%load%%'' can find a data file by trying to append file suffixes configured for the current application, while ''%%save%%'' by default overwrites the file the object was initially loaded from. ''%%load_data%%'' and ''%%save_data%%'' always require full file name and do not try to guess anything.
+===== Pretty formatting of JSON files =====
+Files produced by ''%%save%%'' and ''%%save_data%%'' are very dense, they don't contain line breaks and other redundant whitespaces. The order of properties in a big object is random, they can be arbitrarily reshuffled with every new ''%%save%%'' operation. If you are going to keep your data files under version control like git, or just want to have a look into such file, create it with an option ''%%canonical%%'':
+<code perl>
+> save($p,"myPrettyObject.poly",canonical=>true);
+</code>
+===== Saving visualized objects =====
+Furthermore, most visualization methods provide an option to save the visualized object in a suitable format. Consult the [[user_guide:intro_tutorial#getting_help|F1 help]] for information on the file format and further options.
+To save the cube visualized via JReality in a new file called ''%%mycube.bsh%%'', do this:
+<code perl>
+jreality(cube(3)->VISUAL,File=>"mycube");
+</code>
+To save the cube as a TiKz file named ''%%mycube.tikz%%'' that you can e.g. import in a LaTeX document, do this instead:
+<code perl>
+tikz(cube(3)->VISUAL,File=>"mycube");
+</code>
+===== Handling arbitrary files =====
+Of course, it is also possible to load data from files in other formats. For this purpose use the standard Perl functions for reading and writing. Here is an example:
+Assume you want to load some points stored in the file points.txt which looks like this: 1 0 0 0 1 1 0 0 1 0 1 0 1 1 1 0 1 0 0 1 1 1 0 1 1 0 1 1 1 1 1 1 For the sake of the example, let's create this file:
+<code perl>
+> open(my $f, ">", "points.txt"); print $f "1 0 0 0\n1 1 0 0\n1 0 1 0\n1 1 1 0\n1 0 0 1\n1 1 0 1\n1 0 1 1\n1 1 1 1\n"; close $f;
+</code>
+To read this file try the following:
+<code perl>
+> open(INPUT, "<", "points.txt");
+> while(<INPUT>){
+>   print $_;
+> }
+> close(INPUT);
+0 0 0
+1 0 0
+0 1 0
+1 1 0
+0 0 1
+1 0 1
+0 1 1
+1 1 1
+</code>
+''%%<INPUT>%%'' is a perl input iterator reading the file line by line. Variable ''%%$_%%'' refers to the current line within this loop; it has a plain string value.
+A reasonable task could be to store the points from the file as a matrix. This can be done immediately, because the matrix constructor called with a list of values interprets each value as a matrix line:
+<code perl>
+> open(INPUT, "<", "points.txt");
+> $matrix=new Matrix<Rational>(<INPUT>);
+> close(INPUT);
+> print $matrix;
+0 0 0
+1 0 0
+0 1 0
+1 1 0
+0 0 1
+1 0 1
+0 1 1
+1 1 1
+</code>