StackOverflow2013

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copied!<p>Rather than continue to defend why I need this, I decided to just write it and share. I based this off of an implementation of Python's <code>os.path.relpath</code> at <a href="http://mail.python.org/pipermail/python-list/2009-August/1215220.html">http://mail.python.org/pipermail/python-list/2009-August/1215220.html</a></p> <pre><code>@implementation NSString (Paths) - (NSString*)stringWithPathRelativeTo:(NSString*)anchorPath { NSArray *pathComponents = [self pathComponents]; NSArray *anchorComponents = [anchorPath pathComponents]; NSInteger componentsInCommon = MIN([pathComponents count], [anchorComponents count]); for (NSInteger i = 0, n = componentsInCommon; i < n; i++) { if (![[pathComponents objectAtIndex:i] isEqualToString:[anchorComponents objectAtIndex:i]]) { componentsInCommon = i; break; } } NSUInteger numberOfParentComponents = [anchorComponents count] - componentsInCommon; NSUInteger numberOfPathComponents = [pathComponents count] - componentsInCommon; NSMutableArray *relativeComponents = [NSMutableArray arrayWithCapacity: numberOfParentComponents + numberOfPathComponents]; for (NSInteger i = 0; i < numberOfParentComponents; i++) { [relativeComponents addObject:@".."]; } [relativeComponents addObjectsFromArray: [pathComponents subarrayWithRange:NSMakeRange(componentsInCommon, numberOfPathComponents)]]; return [NSString pathWithComponents:relativeComponents]; } @end </code></pre> <p>Note that there are some cases this won't correctly handle. It happens to handle all the cases I need. Here is the skimpy unit test I used to verify correctness:</p> <pre><code>@implementation NSStringPathsTests - (void)testRelativePaths { STAssertEqualObjects([@"/a" stringWithPathRelativeTo:@"/"], @"a", @""); STAssertEqualObjects([@"a/b" stringWithPathRelativeTo:@"a"], @"b", @""); STAssertEqualObjects([@"a/b/c" stringWithPathRelativeTo:@"a"], @"b/c", @""); STAssertEqualObjects([@"a/b/c" stringWithPathRelativeTo:@"a/b"], @"c", @""); STAssertEqualObjects([@"a/b/c" stringWithPathRelativeTo:@"a/d"], @"../b/c", @""); STAssertEqualObjects([@"a/b/c" stringWithPathRelativeTo:@"a/d/e"], @"../../b/c", @""); STAssertEqualObjects([@"/a/b/c" stringWithPathRelativeTo:@"/d/e/f"], @"../../../a/b/c", @""); } @end </code></pre>

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