使用@avg收集运算符格式化NSPredicate的字符串 [英] Format string for NSPredicate with @avg collection operator

问题描述

有一种方法来构造一个NSPredicate，所以下面的数组可以过滤平均分数大于，比如5？

Is there a way to construct an NSPredicate so the following array can be filtered by average score larger than, say, 5?

NSArray *objs = @[
@{@"scores":@[@3, @5, @2]},
@{@"scores":@[@5, @2, @8, @9]},
@{@"scores":@[@7, @1, @4]}
];

我尝试过各种组合，其中一个看起来最有前途code> @ avg.self 用于通过正常KVC获取数组中数字的平均值）：

I have tried various combinations, of which this one seemed the most promising (considering that the key path @avg.self works to obtain the average value of numbers in an array through normal KVC):

NSPredicate *pred = [NSPredicate predicateWithFormat:@"[e-mail] > 5"];
NSArray     *filterd = [objs filteredArrayUsingPredicate:pred];

我得到的运行时错误如下：

The runtime error I get is the following:

NSUnknownKeyException'，reason：'[< __ NSArrayI 0x10011b7c0> valueForUndefinedKey：]：此类不是键值编码符合关键字avg。

NSUnknownKeyException', reason: '[<__NSArrayI 0x10011b7c0> valueForUndefinedKey:]: this class is not key value coding-compliant for the key avg.

string works： scores。@ count> 3 ，所以至少可以在谓词中使用该集合运算符。

This predicate string works: scores.@count > 3, so at least that collection operator can be used in a predicate.

推荐答案

如果您更改 score。@ avg.self> 5 到得分。@ avg.doubleValue> 5 它会正常工作。

If you change [e-mail] > 5 to [e-mail] > 5 it will work fine.

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