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From Deron Eriksson <deroneriks...@gmail.com>
Subject Re: Matrix non-range indexing should return a scalar
Date Fri, 28 Jul 2017 23:03:20 GMT
Thank you Mike for bringing this up. To me, this definitely makes sense at
the user (DML) level.

For a Java-style pseudocode example, currently we require the user to do
the following:
  int[][] m = int[][]{1,2,3,4};
  int[][] n = m[0][0];
  int x = (int) n;

I feel the following would be more 'natural':
  int[][] m = int[][]{1,2,3,4};
  int x = m[0][0];

If a user asks for a specific cell (and not a range) in DML code, I think
the user clearly wants a value and not a matrix that the user needs to cast
via as.scalar.

Deron



On Fri, Jul 28, 2017 at 3:41 PM, <dusenberrymw@gmail.com> wrote:

> Currently, non-range matrix indexing, such as `X[1,2]`, returns a 1x1
> matrix in SystemML rather than a single scalar value.  This is inconsistent
> with mathematical semantics, and with array indexing semantics of any major
> language, thus leading to confusion for users.
>
> I would like to propose that non-range indexing at the language level,
> such as `X[1,2]`, should return a single scalar value, and range indexing
> of any kind at the language level, including the trivial example
> `X[1:1,2:2]`, should return a matrix.  This would lead to clear semantics
> that are consistent with mathematics and language array indexing, thus
> preventing user confusion.  Additionally, these are the semantics that the
> NumPy project uses.
>
> Interested to hear thoughts from the rest of the community!
>
> -Mike
>
> --
>
> Mike Dusenberry
> GitHub: github.com/dusenberrymw
> LinkedIn: linkedin.com/in/mikedusenberry
>
> Sent from my iPhone.
>
>

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