stan-dev / stan-dev/math

categorical_* functions don't accept row_vectors (it would be good that they could)

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Description

Summary:

The functions for the categorical distribution only accept a column vector, it would be great if it could accept also row vectors.

Description:

I use the categorical distribution to go over a matrix N_obs x N_probabilities, so it's more natural for me to use row vectors than column vectors.

Current functions:

real categorical_lpmf(ints y | vector theta)
real categorical_logit_lpmf(ints y | vector beta)
int categorical_rng(vector theta)

Expected functions:

real categorical_lpmf(ints y | row_vector theta)
real categorical_logit_lpmf(ints y | row_vector beta)
int categorical_rng(row_vector theta)

Current Version:

v2.15.0

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First steps

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  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

Research direction

Locate the categorical_lpmf, categorical_logit_lpmf, and categorical_rng entry points and inspect how their vector arguments are handled. Verify the expected row_vector forms for all three functions and confirm that existing column-vector behavior remains unchanged.

Written by the indexing model from the issue text.

Assessment

Tech stack
cpp
Domain
backend
Issue type
Feature
Difficulty
3/5
Estimated time
1-2 days
Activity status
Stale
Clarity
Mostly clear
Newbie friendliness
45/100

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