CODEWITHSUNDEEP
matlab
Rose Perrone
Rose Perrone

Reputation: 63506

The CLASS function must be called from a class constructor

I'm trying to find the type of a struct field.

I tried to call prod on what I thought was an array, but I got this error:

??? Error using ==> prod
Dimension argument must be a positive integer scalar within indexing range.

So I printed the object in question and found this:

K>> F.val

ans =

   0.110000000000000   0.890000000000000


ans =

   0.590000000000000   0.410000000000000   0.220000000000000   0.780000000000000


ans =

   0.390000000000000   0.610000000000000   0.060000000000000   0.940000000000000

Which is different than the output of an array, which is this:

K>> [0.11 0.89 0.59 0.41 0.22 0.78 0.39 0.61 0.06 0.94]

ans =

  Columns 1 through 4

   0.110000000000000   0.890000000000000   0.590000000000000   0.410000000000000

  Columns 5 through 8

   0.220000000000000   0.780000000000000   0.390000000000000   0.610000000000000

  Columns 9 through 10

   0.060000000000000   0.940000000000000

and when I call class on the object, I get this error:

K>> class(F.val)
??? Error using ==> class
The CLASS function must be called from a class constructor.

How can I find the type of F.val?

Upvotes: 2

Views: 2719

Answers (1)

Jonas
Jonas

Reputation: 74930

F is most likely an array of structures. Thus, calling class(F.val) is like calling class(F(1).val, F(2).val, F(3).val), which is different than the one-input-element syntax.

Use class(F(1).val) to obtain the class of val of the first element of F.

By the way, the error with prod is very likely of similar origin. prod(F(1).val) works fine, however, with two inputs, the second is assumed to be a dimension argument, and that needs to be an integer (which can be of class double, though).

Upvotes: 5

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