Convention for output of tuples
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Assessment
- Difficulty
- 5/5
- Estimated time
- Over a week
- Newbie friendliness
- 35/100
Research direction
Start with the tuple_out.stan example and the test_tuple_out test shown in the issue, then inspect fit.stan_variable("c") and fit.c behavior. Compare array-of-tuples and tuple-of-arrays layouts, and define the resulting sample indexing convention before updating the relevant tests and documentation.
Written by the indexing model from the issue text.
Description
In the develop branch, tuples generated by Stan programs are one-dimensional arrays of tuples. This can make it difficult to access elements of tuples. For example, consider the following test.
def test_tuple_out() -> None:
stan = os.path.join(DATAFILES_PATH, 'tuple_out.stan')
model = CmdStanModel(stan_file=stan)
a = np.random.normal(0, 1, (5, 5))
b = np.random.normal(0, 1, 3)
fit = model.sample({"a": a, "b": b}, fixed_param=True, chains=1,
iter_sampling=20, iter_warmup=1, sig_figs=18)
np.testing.assert_allclose(a, fit.stan_variable("c")[0][0])
np.testing.assert_allclose(b, fit.stan_variable("c")[0][1])
// tuple_out.stan
data {
matrix [5, 5] a;
vector [3] b;
}
generated quantities {
tuple(matrix[5, 5], vector[3]) c;
c.1 = a;
c.2 = b;
}
Then accessing c.1 samples is only possible through list comprehension (there may be some fancy indexing I'm not familiar with).
>>> fit.c.shape
(20,)
>>> fit.c[:, 0]
IndexError: too many indices for array: array is 1-dimensional, but 2 were indexed
Would it make sense to return a tuple of arrays rather than an array of tuples? This would allow accessing samples more easily, e.g., in the above example we'd get
>>> fit.c[0].shape
(20, 5, 5)
This would however go against the convention that the first index refers to samples.
- Dominant language
- Python
- Stars
- 198
- Forks
- 81
- PR merge metrics
- No merged PRs in 30d
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