Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>Here's one way:</p> <pre><code>In[1]:= foo[args___] := Length[{args}] In[2]:= foo[1,2,3,4] Out[2]= 4 </code></pre> <p>When you define a function like this, the pattern <code>args___</code> (with 3 trailing underscores) will match a <a href="http://reference.wolfram.com/mathematica/ref/Sequence.html" rel="nofollow noreferrer"><code>Sequence</code></a> of 0 or more things. You can't use <code>Length</code> on a <code>Sequence</code> and have anything sensible happen, so you should wrap <code>args</code> in a <code>List</code> (the <code>{}</code>) first.</p> <p>However, belisarius is correct. For a lot of iterative operations, it will be easier and more efficient to use built-in higher-order functions like <code>Map</code> and <code>Fold</code>.</p> <p><strong>EDIT to add:</strong> Due to way that Mathematica expressions are built on top of bounds-checked arrays, <code>Length</code> is <em>O</em> (1) in time. This might lead you to believe that <code>foo</code> <strong>also</strong> has <em>O</em> (1) complexity, but you would be wrong. Due to the way pattern-matching works, all of the elements matched by <code>args</code> will be <strong>copied</strong> into the new <code>List</code> that you then pass to <code>Length</code>, making the complexity <em>O</em> (<em>N</em>). This isn't necessarily a huge problem, because using really huge argument lists with a function almost invariably means using <code>Apply</code>, which does an <em>O</em> (<em>N</em>) copy anyway, but it's something you should know.</p> <p><strong>EDIT again to add:</strong> There's another way to do this using <code>Length</code> directly on the expression being evaluated (like most of Mathematica's list-oriented functions, <code>Length</code> can be used on expressions with any head, not just lists). Nothing is copied because no sequences are matched and given new heads, and the function which is having its arguments counted need not have any special attributes like <code>HoldAll</code>. Nonetheless, it is a sleazy hack that exploits a quirk in the pattern-matching machinery by introducing side-effects where side-effects really don't belong, so I would use it with extreme caution, if at all:</p> <pre><code>Module[{n}, expr : foo[___] /; (n = Length[Unevaluated[expr]]; True) := n] </code></pre> <p>The variable <code>n</code> could be global, but <code>Module</code> will create (or at least do a good job faking) lexical closures, so you can at least keep your variables local.</p>
    singulars
    1. This table or related slice is empty.
    1. POMathematica: get number of arguments passed to a function?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. USPillsy
    1. USPillsy
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POMathematica: get number of arguments passed to a function?
      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. VTUpMod
    1. COAs a point of note, I use the above method of turning a `Sequence` into a `List` to process argument lists, in general. With only a single underscore, it is easy to use, but having a named sequence isn't as easy to use directly within a function.
      singulars
      1. PO
      1. USrcollyer
 

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