mixture() doesn't work with single-column arrays

[hrlai]

Hi there, sorry for submitting so many issues lately, but I'm really trying to squeeze a lot from greta now!

I'm playing around with mixture(). One of the examples in ?mixture is

# weights can also be an array, giving different mixing weights
# for each observation (first dimension must be number of components)
dim <- c(5, 4)
weights <- uniform(0, 1, dim = c(2, dim))
b <- mixture(normal(1, 1, dim = dim),
  normal(-1, 1, dim = dim),
  weights = weights
)

I'm trying to mix two distributions that are single-column arrays, but in an attempt to try dim <- c(5, 1) it throws an error:

> dim <- c(5, 1)
> weights <- uniform(0, 1, dim = c(2, dim))
> b <- mixture(normal(1, 1, dim = dim),
+              normal(-1, 1, dim = dim),
+              weights = weights
+ )
Error: the dimension of weights must be either "\033[34m2\033[39mx1" or
"\033[34m2\033[39mx\033[34m\"5x1\"\033[39m"
but was "2x5x1"

Curiously, dim <- c(1, 5) works... did I miss something?

[njtierney]

Hi @hrlai !

Thanks so much for posting these issues, no need to apologise, you're helping make the software better :) so do keep posting. I'm not sure what is going on with the message getting garbled there, I've posted about that here: r-lib/cli#474

I confirm that I get the same error:

#works
library(greta)
#> 
#> Attaching package: 'greta'
#> The following objects are masked from 'package:stats':
#> 
#>     binomial, cov2cor, poisson
#> The following objects are masked from 'package:base':
#> 
#>     %*%, apply, backsolve, beta, chol2inv, colMeans, colSums, diag,
#>     eigen, forwardsolve, gamma, identity, rowMeans, rowSums, sweep,
#>     tapply
dim <- c(5, 4)
weights <- uniform(0, 1, dim = c(2, dim))
#> ℹ Initialising python and checking dependencies, this may take a moment.
#> ✔ Initialising python and checking dependencies ... done!
#> 
b <- mixture(normal(1, 1, dim = dim),
             normal(-1, 1, dim = dim),
             weights = weights)

b
#> greta array (variable following a mixture distribution)
#> 
#>      [,1] [,2] [,3] [,4]
#> [1,]  ?    ?    ?    ?  
#> [2,]  ?    ?    ?    ?  
#> [3,]  ?    ?    ?    ?  
#> [4,]  ?    ?    ?    ?  
#> [5,]  ?    ?    ?    ?

# fails
dim <- c(5, 1)
weights <- uniform(0, 1, dim = c(2, dim))
b <- mixture(normal(1, 1, dim = dim),
             normal(-1, 1, dim = dim),
             weights = weights)
#> Error: the dimension of weights must be either "2x1" or "2x\"5x1\""
#> but was "2x5x1"

# but this works
dim <- c(1,5)
weights <- uniform(0, 1, dim = c(2, dim))
b <- mixture(normal(1, 1, dim = dim),
             normal(-1, 1, dim = dim),
             weights = weights)

^{Created on 2022-06-01 by the reprex package (v2.0.1)}

Session info

sessioninfo::session_info()
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Which is erroring here:

greta/R/mixture.R

Lines 126 to 151 in 112a968

	# drop a trailing 1 from dim, so user doesn't need to deal with it
	# Ugh, need to get rid of column vector thing soon.
	weights_extra_dim <- dim
	n_extra_dim <- length(weights_extra_dim)
	if (weights_extra_dim[n_extra_dim] == 1) {
	weights_extra_dim <- weights_extra_dim[-n_extra_dim]
	}
	# remainder should be 1 or match weights_extra_dim
	w_dim <- weights_dim[-1]
	dim_1 <- length(w_dim) == 1 && w_dim == 1
	dim_same <- all(w_dim == weights_extra_dim)
	if (!(dim_1 | dim_same)) {
	msg <- cli::format_error(
	c(
	"the dimension of weights must be either \\
	{.val {n_distributions}x1} or \\
	{.val {n_distributions}x{paste(dim, collapse = 'x')}}",
	" but was {.val {paste(weights_dim, collapse = 'x')}}"
	)
	)
	stop(
	msg,
	call. = FALSE
	)
	}

I'm not sure why this is erroring, and I don't think I understand the reason for the error handling, since the error message suggests that the dimension of the weights should be either "2x1" or "2x5x1", but then errors saying that the weights were "2x5x1". The comments seem to suggest that it is trying to help by dropping a trailing 1, but in this instance, I think we want that?

@goldingn do you have thoughts on this?