[R] Ordered factors and DBMS
bates at stat.wisc.edu
Thu Oct 4 16:06:21 CEST 2001
"F. Tusell" <etptupaf at bs.ehu.es> writes:
> Is there any way of preserving order of ordered factors when storing a
> table in PostgreSQL?
> I have been using PostgreSQL and the RPgSQL package to store a large
> table with answers such as "Strong disagreement", "Strong agreement",
> "Mild disagreement". "Mild agreement". When reading the table, such
> answers are turned into factors, apparently in reverse alphabetical
> order. If I reorder them using ordered(factor, levels=the order I
> want), everything is fine for the session, but saving the table and
> re-reading it reverts to the original order.
> I have a vague feeling of having seen this asked, but I could not
> locate any references. I looked also B.D. Ripley's "Using Databases
> with R", but this problem is not discussed.
I think it would be difficult to do this in a single table in
PostgreSQL but it could be expressed naturally as two tables and a
join. The first table would contain the data as factor levels and the
second table would give the correspondence between levels and labels.
The join would provide the data as labels by matching the levels.
Another possibility is to define a PostgreSQL data type for this.
MySQL does have this type of structure. They call it an enum
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