谓词逻辑NSPredicate
一般来说这种情况还是蛮多的,比如你从文件中读入了一个array1,然后想把程序中的一个array2中符合array1中内容的元素过滤出来。
正 常傻瓜一点就是两个for循环,一个一个进行比较,这样效率不高,而且代码也不好看。
其实一个循环或者无需循环就可以搞定了,那就需要用搞 NSPredicate这个类了~膜拜此类~
1)例子一,一个循环
NSArray *arrayFilter = [NSArray arrayWithObjects:@"pict", @"blackrain", @"ip", nil]; NSArray *arrayContents = [NSArray arrayWithObjects:@"I am a picture.", @"I am a guy", @"I am gagaga", @"ipad", @"iphone", nil]; |
我想过滤arrayContents的话只要循环 arrayFilter就好了
int i = 0, count = [arrayFilter count]; for(i = 0; i < count; i ++) { NSString *arrayItem = (NSString *)[arrayFilter objectAtIndex:i]; NSPredicate *filterPredicate = [[NSPredicate predicateWithFormat:@"SELF CONTAINS %@", arrayItem]; NSLog(@"Filtered array with filter %@, %@", arrayItem, [arrayContents filteredArrayUsingPredicate:filterPredicate]); } |
当然以上代码中arrayContent最好用mutable 的,这样就可以直接filter了,NSArray是不可修改的。
2)例子二,无需循环
NSArray *arrayFilter = [NSArray arrayWithObjects:@"abc1", @"abc2", nil]; NSArray *arrayContent = [NSArray arrayWithObjects:@"a1", @"abc1", @"abc4", @"abc2", nil]; NSPredicate *thePredicate = [NSPredicate predicateWithFormat:@"NOT (SELF in %@)", arrayFilter]; [arrayContent filterUsingPredicate:thePredicate];
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这样arrayContent过滤出来的就是不包含 arrayFilter中的所有item了。
3)生成文件路径下文件集合列表
NSFileManager *fileManager = [NSFileManagerdefaultManager];NSString *defaultPath = [[NSBundle mainBundle] resourcePath]; NSError *error; NSArray *directoryContents = [fileManager contentsOfDirectoryAtPath:defaultPath error:&error]
4)match的用法
1. 简单比较
NSString *match = @"imagexyz-999.png";NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF == %@", match]; NSArray *results = [directoryContents filteredArrayUsingPredicate:predicate];2. match里like的用法(类似Sql中的用法)NSString *match = @"imagexyz*.png";NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF like %@", match]; NSArray *results = [directoryContents filteredArrayUsingPredicate:predicate];3. 大小写比较 [c]表示忽略大小写,[d]表示忽略重音,可以在一起使用,如下:NSString *match = @"imagexyz*.png";NSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF like[cd] %@", match]; NSArray *results = [directoryContents filteredArrayUsingPredicate:predicate];
4.使用正则 NSString *match = @"imagexyz-\\d{3}\\.png"; //imagexyz-123.pngNSPredicate *predicate = [NSPredicate predicateWithFormat:@"SELF matches %@", match]; NSArray *results = [directoryContents filteredArrayUsingPredicate:predicate];
总结:
1) 当使用聚合类的操作符时是可以不需要循环的
2)当使用单个比较类的操作符时可以一个循环来搞定
PS,例子 一中尝试使用[@"SELF CONTAINS %@", arrayFilter] 来过滤会挂调,因为CONTAINS时字符串比较操作符,不是集合操作符。
Cocoa用NSPredicate描述查询的方式,原理类似于在数据库中进行查询 计算谓词: //基本的查询 NSPredicate *predicate; predicate = [NSPredicate predicateWithFormat: @"name == 'Herbie'"]; BOOL match = [predicate evaluateWithObject: car]; NSLog (@"%s", (match) ? "YES" : "NO"); //在整个cars里面循环比较 predicate = [NSPredicate predicateWithFormat: @"engine.horsepower > 150"]; NSArray *cars = [garage cars]; for (Car *car in [garage cars]) { if ([predicate evaluateWithObject: car]) { NSLog (@"%@", car.name); } } //输出完整的信息 predicate = [NSPredicate predicateWithFormat: @"engine.horsepower > 150"]; NSArray *results; results = [cars filteredArrayUsingPredicate: predicate]; NSLog (@"%@", results); //含有变量的谓词 NSPredicate *predicateTemplate = [NSPredicate predicateWithFormat:@"name == $NAME"]; NSDictionary *varDict; varDict = [NSDictionary dictionaryWithObjectsAndKeys: @"Herbie", @"NAME", nil]; predicate = [predicateTemplate predicateWithSubstitutionVariables: varDict]; NSLog(@"SNORGLE: %@", predicate); match = [predicate evaluateWithObject: car]; NSLog (@"%s", (match) ? "YES" : "NO"); //注意不能使用$VARIABLE作为路径名,因为它值代表值 //谓词字符窜还支持c语言中一些常用的运算符 predicate = [NSPredicate predicateWithFormat: @"(engine.horsepower > 50) AND (engine.horsepower < 200)"]; results = [cars filteredArrayUsingPredicate: predicate]; NSLog (@"oop %@", results); predicate = [NSPredicate predicateWithFormat: @"name < 'Newton'"]; results = [cars filteredArrayUsingPredicate: predicate]; NSLog (@"%@", [results valueForKey: @"name"]); //强大的数组运算符 predicate = [NSPredicate predicateWithFormat: @"engine.horsepower BETWEEN { 50, 200 }"]; results = [cars filteredArrayUsingPredicate: predicate]; NSLog (@"%@", results); NSArray *betweens = [NSArray arrayWithObjects: [NSNumber numberWithInt: 50], [NSNumber numberWithInt: 200], nil]; predicate = [NSPredicate predicateWithFormat: @"engine.horsepower BETWEEN %@", betweens]; results = [cars filteredArrayUsingPredicate: predicate]; NSLog (@"%@", results); predicateTemplate = [NSPredicate predicateWithFormat: @"engine.horsepower BETWEEN $POWERS"]; varDict = [NSDictionary dictionaryWithObjectsAndKeys: betweens, @"POWERS", nil]; predicate = [predicateTemplate predicateWithSubstitutionVariables: varDict]; results = [cars filteredArrayUsingPredicate: predicate]; NSLog (@"%@", results); //IN运算符 predicate = [NSPredicate predicateWithFormat: @"name IN { 'Herbie', 'Snugs', 'Badger', 'Flap' }"]; results = [cars filteredArrayUsingPredicate: predicate]; NSLog (@"%@", [results valueForKey: @"name"]); predicate = [NSPredicate predicateWithFormat: @"SELF.name IN { 'Herbie', 'Snugs', 'Badger', 'Flap' }"]; results = [cars filteredArrayUsingPredicate: predicate]; NSLog (@"%@", [results valueForKey: @"name"]); names = [cars valueForKey: @"name"]; predicate = [NSPredicate predicateWithFormat: @"SELF IN { 'Herbie', 'Snugs', 'Badger', 'Flap' }"]; results = [names filteredArrayUsingPredicate: predicate];//这里限制了SELF的范围 NSLog (@"%@", results); //BEGINSWITH,ENDSWITH,CONTAINS //附加符号,[c],[d],[cd],c表示不区分大小写,d表示不区分发音字符,cd表示什么都不区分 predicate = [NSPredicate predicateWithFormat: @"name BEGINSWITH 'Bad'"]; results = [cars filteredArrayUsingPredicate: predicate]; NSLog (@"%@", results); predicate = [NSPredicate predicateWithFormat: @"name BEGINSWITH 'HERB'"]; results = [cars filteredArrayUsingPredicate: predicate]; NSLog (@"%@", results); predicate = [NSPredicate predicateWithFormat: @"name BEGINSWITH[cd] 'HERB'"]; results = [cars filteredArrayUsingPredicate: predicate]; NSLog (@"%@", results); //LIKE运算符(通配符) predicate = [NSPredicate predicateWithFormat: @"name LIKE[cd] '*er*'"]; results = [cars filteredArrayUsingPredicate: predicate]; NSLog (@"%@", results); predicate = [NSPredicate predicateWithFormat: @"name LIKE[cd] '???er*'"]; results = [cars filteredArrayUsingPredicate: predicate]; NSLog (@"%@", results); |