使用jq改造树形JSON：上移单元素列表项、删除空项

核心目标 #

对类文件/文件夹结构的树形JSON执行两类转换：

• 将仅含单个子项的节点从叶子层级上移（删除中间节点，把子项直接放到原父节点下）
• 删除仅包含基础字段的空节点

结构说明 #

树形结构的组成规则：

• 可选的.item[]数组：用于存储子节点
• 必选的.name字段：节点名称
• 可选的.description字段：节点描述
• 若节点存在除上述字段外的其他额外字段，则该节点不可被删除或合并

示例场景解析 #

• objects/：带有"root f"注释，保留原结构
• external：无额外字段，但包含2个子项，不执行上移操作
• external/buuu和external/biii：含额外字段，保留原节点不做处理
• objects/afolder/methods下的empty和empty2：仅包含name、description或空item数组，属于待删除的空项
• objects/afolder/methods/partner1/operand：仅含单个子项，将子项whetever4上移至partner1下，删除operand节点
• objects/afolder/methods/partner2/operand2：仅含单个子项，将子项whatever3上移至partner2下（与operandx同级），删除operand2节点

转换规则 #

1. jq表达式仅可引用item、name、description字段，不可指定自定义字段（如beep1、keep1等）
2. 保留原有字段的顺序
3. 上移子项时，需放置在原父节点所在的位置
4. 仅当节点下仅有单个子项时才执行上移操作，多子项时不处理

输入示例JSON #

{
    "item": [
        {
            "name": "objects",
            "description": "root f",
            "item": [
                {
                    "name": "external",
                    "item": [
                        {
                            "name": "buuu",
                            "keep1": {}
                        },
                        {
                            "name": "biii",
                            "keep1": {}
                        }
                    ],
                    "description": "Whatever comment."
                },
                {
                    "name": "afolder",
                    "item": [
                        {
                            "name": "methods",
                            "item": [
                                {
                                    "name": "blaaa",
                                    "keep1": {}
                                },
                                {
                                    "name": "empty",
                                    "description": "Whatever2.",
                                    "item": []
                                },
                                {
                                    "name": "partner1",
                                    "item": [
                                        {
                                            "name": "operand",
                                            "item": [
                                                {
                                                    "name": "whetever4",
                                                    "beep1": { },
                                                    "beep2": []
                                                }
                                            ]
                                        }
                                    ]
                                },
                                {
                                    "name": "empty2",
                                    "description": "Whatever3."
                                },
                                {
                                    "name": "partner2",
                                    "item": [
                                        {
                                            "name": "operandx",
                                            "beep2": []
                                        },
                                        {
                                            "name": "operand2",
                                            "item": [
                                                {
                                                    "name": "whatever3",
                                                    "beep1": { },
                                                    "beep2": []
                                                }
                                            ]
                                        }
                                    ]
                                }
                            ]
                        }
                    ]
                }
            ]
        }
    ]
}

预期输出示例JSON #

{
    "item": [
        {
            "name": "objects",
            "description": "root f",
            "item": [
                {
                    "name": "external",
                    "item": [
                        {
                            "name": "buuu",
                            "keep1": {}
                        },
                        {
                            "name": "biii",
                            "keep1": {}
                        }
                    ],
                    "description": "Whatever comment."
                },
                {
                    "name": "afolder",
                    "item": [
                        {
                            "name": "methods",
                            "item": [
                                {
                                    "name": "blaaa",
                                    "keep1": {}
                                },
                                {
                                    "name": "partner1",
                                    "item": [
                                        {
                                            "name": "whetever4",
                                            "beep1": { },
                                            "beep2": []
                                        }
                                    ]
                                },
                                {
                                    "name": "partner2",
                                    "item": [
                                        {
                                            "name": "operandx",
                                            "beep2": []
                                        },
                                        {
                                            "name": "whatever3",
                                            "beep1": { },
                                            "beep2": []
                                        }
                                    ]
                                }
                            ]
                        }
                    ]
                }
            ]
        }
    ]
}

jq解决方案 #

使用递归jq表达式实现转换，逻辑分为清理空节点、合并单子项节点两步：

def clean:
  # 过滤空节点：保留有额外字段或非空子项的节点
  select(
    (keys - ["name", "description", "item"] | length > 0) or
    (.item // [] | length > 0)
  ) |
  # 递归处理子项，合并符合条件的单节点
  (.item // []) |= (
    map(clean) |
    map(
      # 检查是否可合并：无额外字段且仅含单个子项
      if (keys - ["name", "description", "item"] | length == 0) and (.item | length == 1)
      then .item[0]  # 用子项替换当前节点，实现上移
      else .
      end
    )
  );

clean

使用方法 #

将上述表达式保存为clean-tree.jq，执行以下命令：

jq -f clean-tree.jq input.json > output.json

逻辑说明 #

1. 递归清理空节点：通过select语句过滤掉仅含基础字段且无有效子项的节点
2. 合并单子项节点：遍历子项时，判断节点是否无额外字段且仅有一个子项，若是则用子项替换当前节点，完成层级上移
3. 保留字段顺序：jq默认保留原有字段顺序，无需额外处理

内容的提问来源于stack exchange，提问作者Tamás Horváth