从展平字典创建嵌套字典 [英] Creating a nested dictionary from a flattened dictionary

问题描述

我有一个拼合的字典，我想把它做成嵌套的形式，

I have a flattened dictionary which I want to make into a nested one, of the form

flat = {'X_a_one': 10,
        'X_a_two': 20, 
        'X_b_one': 10,
        'X_b_two': 20, 
        'Y_a_one': 10,
        'Y_a_two': 20,
        'Y_b_one': 10,
        'Y_b_two': 20}

我想将其转换为表格

nested = {'X': {'a': {'one': 10,
                      'two': 20}, 
                'b': {'one': 10,
                      'two': 20}}, 
          'Y': {'a': {'one': 10,
                      'two': 20},
                'b': {'one': 10,
                      'two': 20}}}

平面字典的结构应避免歧义出现任何问题.我希望它适用于任意深度的字典，但是性能并不是真正的问题.我见过许多用于平整嵌套字典的方法，但是基本上没有用于嵌套平整字典的方法.存储在字典中的值是标量或字符串，永远不可迭代.

The structure of the flat dictionary is such that there should not be any problems with ambiguities. I want it to work for dictionaries of arbitrary depth, but performance is not really an issue. I've seen lots of methods for flattening a nested dictionary, but basically none for nesting a flattened dictionary. The values stored in the dictionary are either scalars or strings, never iterables.

到目前为止，我已经有了一些可以接受输入的东西

So far I have got something which can take the input

test_dict = {'X_a_one': '10',
             'X_b_one': '10',
             'X_c_one': '10'}

到输出

test_out = {'X': {'a_one': '10', 
                  'b_one': '10', 
                  'c_one': '10'}}

使用代码

def nest_once(inp_dict):
    out = {}
    if isinstance(inp_dict, dict):
        for key, val in inp_dict.items():
            if '_' in key:
                head, tail = key.split('_', 1)

                if head not in out.keys():
                    out[head] = {tail: val}
                else:
                    out[head].update({tail: val})
            else:
                out[key] = val
    return out

test_out = nest_once(test_dict)

但是我在解决如何使其递归地创建字典的所有级别方面遇到了麻烦.

But I'm having trouble working out how to make this into something which recursively creates all levels of the dictionary.

任何帮助将不胜感激！

(关于为什么要执行此操作:我有一个结构等同于嵌套字典的文件，我想将此文件的内容存储在NetCDF文件的属性字典中，以后再检索.但是仅适用于NetCDF允许您将平面字典作为属性，因此我想展开以前存储在NetCDF文件中的字典.)

(As for why I want to do this: I have a file whose structure is equivalent to a nested dict, and I want to store this file's contents in the attributes dictionary of a NetCDF file and retrieve it later. However NetCDF only allows you to put flat dictionaries as the attributes, so I want to unflatten the dictionary I previously stored in the NetCDF file.)

推荐答案

这是我的看法:

def nest_dict(flat):
    result = {}
    for k, v in flat.items():
        _nest_dict_rec(k, v, result)
    return result

def _nest_dict_rec(k, v, out):
    k, *rest = k.split('_', 1)
    if rest:
        _nest_dict_rec(rest[0], v, out.setdefault(k, {}))
    else:
        out[k] = v

flat = {'X_a_one': 10,
        'X_a_two': 20, 
        'X_b_one': 10,
        'X_b_two': 20, 
        'Y_a_one': 10,
        'Y_a_two': 20,
        'Y_b_one': 10,
        'Y_b_two': 20}
nested = {'X': {'a': {'one': 10,
                      'two': 20}, 
                'b': {'one': 10,
                      'two': 20}}, 
          'Y': {'a': {'one': 10,
                      'two': 20},
                'b': {'one': 10,
                      'two': 20}}}
print(nest_dict(flat) == nested)
# True

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