StackOverflow2013

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POCalculating group row at run time of a NSTableView
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copied!<p>I have a <code>NSTableView</code>, filled with song titles.</p> <p>The songs are ordered by artists, so I can display the artist name as a row view.<br /></p> <p><img src="https://i.stack.imgur.com/P9tj4.png" alt="enter image description here"></p> <hr> <h2>Code</h2> <p>Until now, I had to iterate through the table data and manually add the artists to the array.</p> <pre><code>NSMutableArray *songsAndArtists = [NSMutableArray array]; Artist *artist; for (Song *song in self.songs) { if (artist != song.artist) { artist = song.artist; [songsAndArtists addObject:artist]; } [songsAndArtists addObject:song]; } </code></pre> <hr> <p>This can be really slow if you have 1'000 - 5'000 songs.<br /> I haven't really figured out how I could speed up this process.</p> <p>Does anybody have an idea how to calculate this at runtime?</p> <hr> <h2>EDIT</h2> <p>I'll try to clarify what I meant:</p> <p><code>NSTableView</code> supports <strong>group rows</strong>. My table view displays all the songs in CoreData. I'd like to use the group rows to display the artist of the songs, like in the print screen I added above.</p> <p>To do this I have to provide an array with an artist, followed by it's songs, followed by the next artist, and so on.</p> <p>The code above shows how to insert the artists, but it's a pretty time-consuming process.</p> <p>So my question, how can I speed this up?</p> <hr> <h2>HINT</h2> <p>Like <a href="https://stackoverflow.com/users/210171/nielsbot">nielsbot</a> and <a href="https://stackoverflow.com/users/742584/feloneous-cat">Feloneous Cat</a> suggested, iterating through all the artists won't work for me.</p> <p>The user also has the option to search though the library. Therefore, not all the songs should actually appear in the list.</p> <hr> <h2>Solution</h2> <p>I just want you to let you know what the problem was:</p> <p>The problem was, that I actually compared via <code>NSString</code> in the previous version.<br /> Pretty stupid fault...</p> <p>It takes about <strong>0.1 seconds or less</strong> which is great:</p> <pre><code>tableData = [self addGroupRowsToArray:[self allSongs] withKeyPath:@"artist"]; - (NSArray *)addGroupRowsToArray:(NSArray *)array withKeyPath:(NSString *)keyPath { NSMutableArray *mixedArray = [NSMutableArray array]; id groupRowItem; for (id arrayItem in array) { if (groupRowItem != [arrayItem valueForKeyPath:keyPath]) { groupRowItem = [arrayItem valueForKeyPath:keyPath]; [mixedArray addObject:groupRowItem]; } [mixedArray addObject:arrayItem]; } return mixedArray; } </code></pre>

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