Rust

Question

我正在尝试拆分一堆 (50+) 个 json 文件，为此我想根据文件名的元素按频率对它们的值进行分类。我不仅在这样做，而且在某种程度上是作为一个 Rust 新手来做的，因为它在 Python 中做起来不够有趣。

为了便于解释，让我们想象这样的文件：

a-b-c-d.json
{
    "var":"foo",
    "array": [
        'one',
        'two'
    ]
}
b-c-d-f.json
{
    "var":"bar",
    "array": [
        'one',
        'three'
    ]
}

在处理完这两个文件之后，我想要得到的数据结构是这样的（请注意，这很可能是我的第一个错误）：

{
  'a' : {
    'var' : { 
      'foo': 1
    }, 'array' : {
      'one': 1, 'two': 1 
    }
  },
  'b' : {
    'var' : { 
      'foo': 1,
      'bar': 1
    }, 'array' : {
      'one': 2, 'two': 1, 'three': 1
    }
  }
(also 'c', 'd' and 'f') - I hope the intention is clear with this small example
}

我的伪代码大致是这样的：

每个 json 个文件
将名称分成几部分，按“-”
对于 json 文件中的每个元素（键：值）
将其作为出现次数添加到result[part][key][value]中

因此，结果变量的类型将是 HashMap<String, HashMap<String, HashMap<String, i8>>>

我遇到错误的（实际）代码是：

type ComponentValueElement = HashMap<String, i8>;
type ComponentElement = HashMap<String, ComponentValueElement>;
type ComponentMap = HashMap<String, ComponentElement>;
(...)
fn increase_ocurrence_of_element_in_configuration(component: &String, element: &String, value: &String, final_component_map: &mut ComponentMap) {
    final_component_map.entry(component.into()).or_insert( HashMap::new() );
    final_component_map[component].entry(element.into()).or_insert(HashMap::new());
    final_component_map[component][element].entry(value.into()).or_insert(0);

    final_component_map[component][element][value] += 1;
}

错误是：

<final_component_map[component]>.entry(element.into()).or_insert(HashMap::new());

cannot borrow data in an index of `std::collections::HashMap<std::string::String, std::collections::HashMap<std::string::String, std::collections::HashMap<std::string::String, i8>>>` as mutable

cannot borrow as mutable

help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `std::collections::HashMap<std::string::String, std::collections::HashMap<std::string::String, std::collections::HashMap<std::string::String, i8>>>`

<final_component_map[component][element]>.entry(value.into()).or_insert(0);

cannot borrow data in an index of `std::collections::HashMap<std::string::String, std::collections::HashMap<std::string::String, i8>>` as mutable

cannot borrow as mutable

help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `std::collections::HashMap<std::string::String, std::collections::HashMap<std::string::String, i8>>`

<final_component_map[component][element][value]> += 1;

cannot assign to data in an index of `std::collections::HashMap<std::string::String, i8>`

cannot assign

help: trait `IndexMut` is required to modify indexed content, but it is not implemented for `std::collections::HashMap<std::string::String, i8>`

我原以为在 Rust 中写入 Maps 会更容易 :D 我到底需要做什么才能让我漂亮的嵌套 HashMap 充满值？

非常感谢！

Answer 1

Entry API 的部分要点是您可以更改条目而无需再次查找。您可以像这样将这些查找链接在一起：

fn increase_ocurrence_of_element_in_configuration(
    component: &str,
    element: &str,
    value: &str,
    final_component_map: &mut ComponentMap,
) {
    *final_component_map
        .entry(component.into())
        .or_default()
        .entry(element.into())
        .or_default()
        .entry(value.into())
        .or_default() += 1;
}

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collections

hashmap