Question regarding MX files

Example:

I save data to a MX file, like:

a=Range[100];
b=Range[1000];

Export["data.mx", {a,b}, "MX"];


Can I after importing the data:

data = Import["data.mx", "MX"];


also retrieve the names of the variables a,b?

No, because those names were never saved into the file.

If you want the names saved too, you can use DumpSave instead of Export for saving, and Get instead of Import for loading. In this case, a and b will be overwritten upon Get. I do not like this method because I need to remember those names, and because I consider overwriting dangerous.

Personally I would export an association instead of a list:

<|"a" -> a, "b" -> b|>


This way I can make the structure of the data self-explanatory.

• Could I do this: Export["data.mx", <|"a" -> a, "b" -> b|>, "MX"];? and reading would be: data = Import["data.mx"]? After reading how do I assign a=... and b=...? – lio May 10 '17 at 13:57
• @lio Yes, that is what I meant I would do. But the whole reason why I suggested associations was to avoid assigning. If you want to assign a and b after reading, then I suggest you use DumpSave/Get. – Szabolcs May 10 '17 at 13:59
• Thank you for the explanation ... – lio May 10 '17 at 19:36
• @lio To be fair, you can set values based on an association, but it requires something a bit more advanced: setName[name_String, value_] := ToExpression[name, InputForm, Function[s, s = value, HoldAll]] Now setName["a", 1] sets the value of a to 1. So you can do KeyValueMap[setName, <|"a" -> 1, "b" -> 2|>] to set a to 1 and b to 2. – Szabolcs May 10 '17 at 19:40