Dynamically group flattened JSON into nested JSON object-CodePudding

Suppose I have the following JSON array:

[
    {
        "MainCategory": "1",
        "SubCategory": "a",
        "Value": "val1"
    },
    {
        "MainCategory": "1",
        "SubCategory": "a",
        "Value": "val2"
    },
    {
        "MainCategory": "1",
        "SubCategory": "b",
        "Value": "val3"
    },
    {
        "MainCategory": "2",
        "SubCategory": "a",
        "Value": "val4"
    },
    {
        "MainCategory": "2",
        "SubCategory": "b",
        "Value": "val5"
    },
    {
        "MainCategory": "2",
        "SubCategory": "b",
        "Value": "val6"
    }
]

And would like to convert it into the following multidimensional object in JavaScript (no Lodash):

{
    "1":{
        "a": [
            "val1",
            "val2"
        ],
        "b": [
            "val3"
        ]
    },
    "2":{
        "a": [
            "val4"
        ],
        "b": [
            "val5",
            "val6"
        ]
    }
}

I figure I can do it with a foreach, but I'm trying to do it using the reduce function (HOPING that is the right one to use here) and just not getting the right syntax.

My current GUESS (not working) is something along the lines of:

const newJson = CurrentJson.reduce((result, {MainCategory, SubCategory, Value}) => {
    (result[MainCategory][SubCategory] = result[MainCategory][SubCategory] || [])
    .push(Value);

    return result;
}, {});

How can I do this?

CodePudding user response：

You may use reduce as follows;

var data = [ { "MainCategory": "1"
             , "SubCategory": "a"
             , "Value": "val1"
             }
           , { "MainCategory": "1"
             , "SubCategory": "a"
             , "Value": "val2"
             }
           , { "MainCategory": "1"
             , "SubCategory": "b"
             , "Value": "val3"
             }
           , { "MainCategory": "2"
             , "SubCategory": "a"
             , "Value": "val4"
             }
           , { "MainCategory": "2"
             , "SubCategory": "b"
             , "Value": "val5"
             }
           , { "MainCategory": "2"
             , "SubCategory": "b"
             , "Value": "val6"
             }
           ],
   res  = data.reduce((r,o) => ( r[o.MainCategory] ? r[o.MainCategory][o.SubCategory] ? r[o.MainCategory][o.SubCategory].push(o.Value)
                                                                                      : r[o.MainCategory][o.SubCategory] = [o.Value]
                                                   : r[o.MainCategory] = {[o.SubCategory]: [o.Value]}
                               , r
                               ) ,{});
  console.log(res);

CodePudding user response：

You can use a reducer to iterate over the original JSON and build up the new object.

const json = [
    {
        "MainCategory": "1",
        "SubCategory": "a",
        "Value": "val1"
    },
    {
        "MainCategory": "1",
        "SubCategory": "a",
        "Value": "val2"
    },
    {
        "MainCategory": "1",
        "SubCategory": "b",
        "Value": "val3"
    },
    {
        "MainCategory": "2",
        "SubCategory": "a",
        "Value": "val4"
    },
    {
        "MainCategory": "2",
        "SubCategory": "b",
        "Value": "val5"
    },
    {
        "MainCategory": "2",
        "SubCategory": "b",
        "Value": "val6"
    }
]

const newJson = json.reduce((prev, curr) => {
  // Check for the MainCategory first
  if (prev[curr.MainCategory] === undefined) {
    prev[curr.MainCategory] = {
      [curr.SubCategory]: [] // Add the SubCategory key and define as empty array
    }
  }
  
  // Check if we have the SubCategory
  if (prev[curr.MainCategory][curr.SubCategory] === undefined) {
    prev[curr.MainCategory][curr.SubCategory] = [] // define as empty array
  }

  // Push the Value
  prev[curr.MainCategory][curr.SubCategory].push(curr.Value)
  
  return prev
}, {})

console.log(newJson)