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pik-piam / gdx

R package | readGDX package for R
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readGDX() returns alias, not set #7

Open 0UmfHxcvx5J7JoaOhFSs5mncnisTJJ6q opened 4 months ago

0UmfHxcvx5J7JoaOhFSs5mncnisTJJ6q commented 4 months ago

https://github.com/pik-piam/gdx/blob/6a32a336ade7bfc7459ffda9215db152c6fe5096/R/readGDX.R#L221 What is the rationale for this? Sets and their aliases are used transparently in GAMS, why not here?

tscheypidi commented 4 months ago

sorry, what is your problem here?

0UmfHxcvx5J7JoaOhFSs5mncnisTJJ6q commented 4 months ago

In GAMS there is no difference in using a set, or an alias for a set.

Set foo / 1 * 2 /;

alias(foo, bar);

display foo, bar;

execute_unload "foobar.gdx", foo, bar;

It says that it is an alias, but displays the values all the same.

----      5 SET foo  
1,    2
----      5 SET bar  Aliased with foo
1,    2

But reading an alias with readGDX() does not return the values of the set:

> str(readGDX('foobar.gdx', 'foo'))
 chr [1:2] "1" "2"
 - attr(*, "gdxdata")=List of 5
  ..$ name   : chr "foo"
  ..$ type   : chr "set"
  ..$ form   : chr "sparse"
  ..$ domains: chr "*"
  ..$ domInfo: chr "none"
 - attr(*, "description")= chr ""

> str(readGDX('foobar.gdx', 'bar'))
List of 3
 $ name    : chr "bar"
 $ type    : chr "alias"
 $ aliasFor: chr "foo"

So users cannot simply look up (something that looks like) a set in GAMS (say in the definition of an equation) and use that with readGDX(). They have to first check if that is an alias. Since this is an deliberate choice (followAlias = FALSE is not the default), I wonder why that is.