Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>It's a Cartesian product of Cartesian products:</p> <pre><code>var groups = from x in (from v in values from s in states select new {v,s}) group x by x.v into gx select gx; var perms = from a in groups[0] from b in groups[1] from c in groups[2] select new {a,b,c}; </code></pre> <p>The groups query produces a Lookup (conceptually a read-only Dictionary of IEnumerables) containing the simple Cartesian product of all values and states (6 elements), grouped by their value. Then, the second query produces a Cartesian product of the elements of the Cartesian product taken three at a time, one from each group in the Lookup. </p> <p>To make this work with an unknown number of dimensions would be tricky; if you don't absolutely have to make it work that way I would avoid it. I think the most elegant way would be to define a set of extension methods for the System.Tuple generic classes:</p> <pre><code>public static Tuple&lt;T1,T2&gt; Append(this Tuple&lt;T1&gt; tuple, T2 addend) { return Tuple.Create(tuple.Item1, addend); } public static Tuple&lt;T1,T2, T3&gt; Append(this Tuple&lt;T1,T2&gt; tuple, T3 addend) { return Tuple.Create(tuple.Item1, tuple.Item2, addend); } ... </code></pre> <p>Then, you can take these helpers and use them in a looped version of the second query:</p> <p>var perms = from a in groups[0] select Tuple.Create(a);</p> <p>foreach(var group in groups.Skip(1)) perms = from a in perms from b in group select a.Append(b);</p> <p>This will produce an enumerable of Tuples of the required length, containing the elements of the anonymous type produced in the first query (which can be refactored to produce strongly-typed 2-item Tuples if you wish). You may have an issue with using the perms collection variable to refer to collections of ever-growing Tuples; this is the tricky part.</p>
    singulars
    1. This table or related slice is empty.
    1. POc# combinations with linq
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USKeithS
    1. USKeithS
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POc# combinations with linq
      singulars
      1. PTQuestion
    1. This table or related slice is empty.
    1. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    2. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. PO
      1. This table or related slice is empty.
      1. VTAcceptedByOriginator
    1. COI'm somewhat confused by this answer. I think it needs to be "group x by" in the groups query? Also how does gx get to the second query? The fact that you're using indices 0 1 2 explicitly makes me think that this won't handle varying values array sizes? (Sorry, I'm pretty new to linq, so might be missing something obvious).
      singulars
      1. PO
      1. USuser673679
    2. COTrue on all counts; I updated the group by clause and the references to the grouped data. To make this work with an unknown number of dimensions would be tricky, but possible; basically you would loop through a query that took the result of the previous query and Cartesian-joined the next dimension to each result. The trick would be flattening that structure back out from these nested arrays or anonymous types back into a one-dimensional collection of tuples.
      singulars
      1. PO
      1. USKeithS
    3. COThanks for the edits. I had to use .ToArray() in order to be able to index the groups variable. I'll have a go at varying the dimensions and see what I can come up with.
      singulars
      1. PO
      1. USuser673679
 

Querying!

 
Guidance
A row detail

Detail views are divided into sections. All the information in the data section comes from columns in the selected row. The other sections display data from other, related rows.

Related data can be related in a to-one or a to-many fashion. Captions of data related in a to-many fashion link to a list view showing a filtered view of the table.

Try moving around until you find a non-empty to-many entry and click on the label to get to one. You can move back to the root by clicking on the database name in the header.

SQuiL has stopped working due to an internal error.

If you are curious you may find further information in the browser console, which is accessible through the devtools (F12).

Reload