Databases
StackOverflow2013
Postsdbo
PO
 

Note that there are some explanatory texts on larger screens.

plurals
  1. PO
    primarykey
    data
    text
    <p>I agree with <a href="https://stackoverflow.com/questions/1041620/most-efficient-way-to-erase-duplicates-and-sort-a-c-vector/1041874#1041874">R. Pate</a> and <a href="https://stackoverflow.com/questions/1041620/most-efficient-way-to-erase-duplicates-and-sort-a-c-vector/1041700#1041700">Todd Gardner</a>; a <a href="http://en.cppreference.com/w/cpp/container/set" rel="noreferrer"><code>std::set</code></a> might be a good idea here. Even if you're stuck using vectors, if you have enough duplicates, you might be better off creating a set to do the dirty work.</p> <p>Let's compare three approaches:</p> <p><strong>Just using vector, sort + unique</strong></p> <pre><code>sort( vec.begin(), vec.end() ); vec.erase( unique( vec.begin(), vec.end() ), vec.end() ); </code></pre> <p><strong>Convert to set (manually)</strong></p> <pre><code>set&lt;int&gt; s; unsigned size = vec.size(); for( unsigned i = 0; i &lt; size; ++i ) s.insert( vec[i] ); vec.assign( s.begin(), s.end() ); </code></pre> <p><strong>Convert to set (using a constructor)</strong></p> <pre><code>set&lt;int&gt; s( vec.begin(), vec.end() ); vec.assign( s.begin(), s.end() ); </code></pre> <p>Here's how these perform as the number of duplicates changes:</p> <p><img src="https://i.stack.imgur.com/gGgtR.png" alt="comparison of vector and set approaches"></p> <p><strong>Summary</strong>: when the number of duplicates is large enough, <em>it's actually faster to convert to a set and then dump the data back into a vector</em>. </p> <p>And for some reason, doing the set conversion manually seems to be faster than using the set constructor -- at least on the toy random data that I used.</p>
    singulars
    1. This table or related slice is empty.
    1. POWhat's the most efficient way to erase duplicates and sort a vector?
      singulars
      1. PTQuestion
    1. PTAnswer
    1. This table or related slice is empty.
    1. USNate Kohl
    plurals
    1. This table or related slice is empty.
    1. This table or related slice is empty.
    1. POWhat's the most efficient way to erase duplicates and sort a vector?
      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. COWhy convert back to a vector?
      singulars
      1. PO
      1. USLogan Capaldo
    2. COI'm shocked that the constructor approach is consistently measurably worse than manual. You would that apart from some tiny constant overhead, it would just do the manual thing. Can anyone explain this?
      singulars
      1. PO
      1. USAri
    3. COQuestion: Could this line in your first approach: vec.erase( unique( vec.begin(), vec.end() ), vec.end() ); be replaced with: with: vec.resize( unique (vec.begin(), vec.end()) - vec.begin() ) and if so, would it be any faster in large vector?
      singulars
      1. PO
      1. USDan
 

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