Databases
StackOverflow2013
Postsdbo
POCan I create an array in Ruby with default values?
 

Note that there are some explanatory texts on larger screens.

plurals
  1. POCan I create an array in Ruby with default values?
    primarykey
    data
    text
    <p>Perl is pretty nice about default values:</p> <pre><code>: jmglov@laurana; perl -e '@foo; printf "%d\n", $foo[123]' 0 : jmglov@laurana; perl -e '%foo; printf "%d\n", $foo{bar}' 0 </code></pre> <p>Ruby can do the same, at least for hashes:</p> <pre><code>&gt;&gt; foo = Hash.new(0) =&gt; {} &gt;&gt; foo[:bar] =&gt; 0 </code></pre> <p>But the same seemingly does not work for arrays:</p> <pre><code>&gt;&gt; foo = Array.new(0) =&gt; [] &gt;&gt; foo[123] =&gt; nil &gt;&gt; foo[124] = 0 =&gt; 0 &gt;&gt; foo[456] = 0 =&gt; 0 &gt;&gt; foo[455,456] =&gt; [nil, 0] </code></pre> <p>Is it possible to supply a default value for arrays, so when they are auto-extended, they're filled with 0 instead of nil?</p> <p>Of course I can work around this, but at a cost to expressiveness:</p> <pre><code>&gt;&gt; foo[457,458] = 890, 321 =&gt; [890, 321] &gt;&gt; foo[456] += 789 NoMethodError: You have a nil object when you didn't expect it! You might have expected an instance of Array. The error occurred while evaluating nil.+ &gt;&gt; foo.inject(0) {|sum, i| sum += (i || 0) } =&gt; 1211 &gt;&gt; foo.inject(:+) NoMethodError: You have a nil object when you didn't expect it! You might have expected an instance of Array. The error occurred while evaluating nil.+ </code></pre> <p><strong>Update 1:</strong> One of my colleagues pointed out that I can use <code>#compact</code> to solve the <code>#inject</code> issue, and <code>#to_i</code> to solve the standard element-at-index issue:</p> <pre><code>&gt;&gt; foo.include? nil =&gt; true &gt;&gt; foo.compact.inject(:+) =&gt; 1211 &gt;&gt; foo[456,457] =&gt; [0, 890, 321] &gt;&gt; foo[455..457] =&gt; [nil, 0, 890] &gt;&gt; foo[455..457].map(&amp;:to_i) =&gt; [0, 0, 890] </code></pre> <p><strong>Update 2:</strong> Thanks to <a href="https://stackoverflow.com/users/38765/andrew-grimm">Andrew Grimm</a> for a solution to the <code>+=</code> issue:</p> <pre><code>&gt;&gt; foo = [] =&gt; [] &gt;&gt; def foo.[](i) &gt;&gt; fetch(i) {0} &gt;&gt; end =&gt; nil &gt;&gt; foo[4] =&gt; 0 &gt;&gt; foo =&gt; [] &gt;&gt; foo[4] += 123 =&gt; 123 &gt;&gt; foo =&gt; [nil, nil, nil, nil, 123] </code></pre> <p><strong>Update 3:</strong> this is starting to look like whack-a-mole!</p> <pre><code>&gt;&gt; foo =&gt; [nil, nil, nil, nil, 123] &gt;&gt; foo[-2..-1] TypeError: can't convert Range into Integer </code></pre> <p>But we can deal with that:</p> <pre><code>&gt;&gt; def foo.[](index) &gt;&gt; if index.is_a? Range &gt;&gt; index.map {|i| self[i] } &gt;&gt; else ?&gt; fetch(index) { 0 } # default to 0 if no element at index; will not cause auto-extension of array &gt;&gt; end &gt;&gt; end =&gt; nil &gt;&gt; foo =&gt; [nil, nil, nil, nil, 123] &gt;&gt; foo[-2..-1] =&gt; [nil, 123] </code></pre> <p>I now have to admit (sheepishly) that I'll subclass <code>Array</code> to avoid cluttering my code:</p> <pre><code>class MyClass class ArrayWithDefault &lt; Array def [](index) if index.is_a? Range index.map {|i| self[i] } else fetch(index) { 0 } # default to 0 if no element at index; will not cause auto-extension of array end end end end </code></pre> <p>Thanks for all the creative solutions. TIMTOWTDI indeed!</p>
    singulars
    1. PO
      singulars
      1. PTAnswer
    1. This table or related slice is empty.
    1. PTQuestion
    1. USCommunity
    1. USJosh Glover
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. PO
      singulars
      1. PTAnswer
    2. PO
      singulars
      1. PTAnswer
    3. PO
      singulars
      1. PTAnswer
    1. VO
      singulars
      1. POCan I create an array in Ruby with default values?
      1. USSimon Woker
      1. VTFavorite
    2. VO
      singulars
      1. POCan I create an array in Ruby with default values?
      1. This table or related slice is empty.
      1. VTUpMod
    3. VO
      singulars
      1. POCan I create an array in Ruby with default values?
      1. This table or related slice is empty.
      1. VTUpMod
    1. COIf you need a sparse array, what's wrong with using a hash with integer keys?
      singulars
      1. POCan I create an array in Ruby with default values?
      1. USSimon
    2. COI wonder if any PHP developers have complained that their array/hash data structure doesn't exist in Ruby.
      singulars
      1. POCan I create an array in Ruby with default values?
      1. USAndrew Grimm
    3. COSimon: I went with a hash in the first place, but there're a pain with some of the #maps and #injects I need to do.
      singulars
      1. POCan I create an array in Ruby with default values?
      1. USJosh Glover
 

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