使用比较器对向量进行排序,该比较器会动态更改其行为 [英] Sort a vector with a comparator which changes its behavior dynamically
问题描述
我有一个自定义结构的向量和一个属性列表,可用于按降序对向量进行排序.例如:
I have a vector of a custom struct and a list of attributes to use for ordering that vector in descending priority. For example:
struct TheStruct {
artist: String,
title: String,
date: String,
}
let order_vec: Vec<String> = vec!["artist".to_string(),"title".to_string(),"date".to_string()];
let item_vec: Vec<TheStruct> = Vec::new();
我希望向量按order_vec
的顺序排序.在此示例中,首先应按艺术家名称排序,当相等时,应按标题进行排序.由于order_vec
是动态变化的,因此我不想对这种顺序进行硬编码.
I want the vector to be ordered as given by order_vec
. In this example, it should first be ordered by the artists name, when this is equal it should be ordered by the title. I do not want to hard-code this ordering as order_vec
changes dynamically.
我发现Vec::sort_by
具有比较功能.如何动态生成该函数?没有sort_by
,有没有办法做到这一点?
I found Vec::sort_by
which takes a compare function. How do I dynamically generate that function? Is there a way to do this without sort_by
?
推荐答案
如何动态生成该函数
How do I dynamically generate that function
你不知道.您有一个内部具有动态行为的特定闭包.
You don't. You have a specific closure that has dynamic behavior inside of it.
在这里,我们有一系列要应用的列表.当我们需要比较两个项目时,我们遍历列表.我们使用 Ordering::then_with
仅应用先前比较为Equal
时的比较:
Here, we have a list of sorts to apply. When we need to compare two items, we iterate through the list. We use Ordering::then_with
to only apply the comparison when the previous comparison was Equal
:
use std::cmp::Ordering;
#[derive(Debug, Copy, Clone)]
enum Field {
Artist,
Title,
Date,
}
struct TheStruct {
artist: String,
title: String,
date: String,
}
fn main() {
let mut items: Vec<TheStruct> = vec![];
use Field::*;
let orders = vec![Artist, Title];
items.sort_by(|a, b| {
orders.iter().fold(Ordering::Equal, |acc, &field| {
acc.then_with(|| {
match field {
Artist => a.artist.cmp(&b.artist),
Title => a.title.cmp(&b.title),
Date => a.date.cmp(&b.date),
}
})
})
})
}
我为这些字段使用了一个枚举,因为当一种类型的字段是未知字段时,我不想处理该做什么.
I used an enum for the fields because I didn't want to deal with what to do when one of the sorts is an unknown field.
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