I'm looking for a way to get the type of an object:
TypeOf["x"] -> String
TypeOf[1] -> Integer
Or something along those lines.
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asked May 7, 2016 at 20:21
2 Answers
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Example:
list = {1, 2, 3};
integer = 1;
real = 0.1;
Head @ list
Head @ integer
Head @ real
Output:
List
Integer
Real
Reference
answered May 7, 2016 at 20:38
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(Post adapted after comments.)
Mathematica 10 introduced a new type system local to Dataset, that's used like this:
Needs["TypeSystem`"]
DeduceType[{1, Sqrt[2], "test", {1, Sqrt[2], 3}, {1, 2, 3}}]
In this type system a type is not the same as Head[expr]. In this framework the head of an atomic value is instead retrieved by TypeAtoms:
But yes, for what you want to do you still need Head.
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DeduceTypeis still undocumented. What are actual use cases for this new type system? $\endgroup$ May 7, 2016 at 20:58 -
3$\begingroup$ This new type system serves primarily
Dataset. It is not on the same fundamental level as Mathematica's core "type system", of whichHeadis part. It has a status of specific type system used by one or several application modules internally, and has no meaning in a more general context of fundamental Mathematica language / building blocks. $\endgroup$ May 7, 2016 at 21:16 -
$\begingroup$ @AlexeyPopkov So far it seems that it is mostly useful for debugging problems with
Dataset, WReach has invoked it in several of his answers to explain different unintuitive behaviors. $\endgroup$– C. E.May 7, 2016 at 21:18 -
$\begingroup$ @LeonidShifrin It is true, but within this framework they refer to
Integer,Realetc. as type atoms, not as types. So whether it is intentional or not they have introduced a new terminology for these labels. Yes, this is nitpicking. I see this as an opportunity to mentionTypeSystemto readers who may not know about it. $\endgroup$– C. E.May 7, 2016 at 21:25 -
2$\begingroup$ Each module is free to define its own notion of types, for its own purposes. For example,
Compilealso has a type system, which is different from either the newTypeSystemor the core Mathematica type system. BothCompile's type system and the newTypeSystemare incomplete - there are types they can't describe (but core Mathematica can). I agree that it is good to mention these, but the question about types in Mathematica in general has a clear and unique answer, and that answer is - atoms and normal expressions, where heads of expressions one may interpret as non-atomic types. $\endgroup$ May 7, 2016 at 21:32
Head. $\endgroup$