Group list of objects by JSON key

Question

I am trying to reformat my list of objects by grouping a certain key pair in javascript.

Data Format

[{
    "sccode": "sccode1",
    "val": "1ADA"
}, {
    "sccode": "sccode2",
    "val": "1ADB"
}, {
    "sccode": "sccode1",
    "val": "1ADC"
}]

Expected Result

[{
        "scCode": "sccode1",
        "valCodes": ["1ADA", "1ADC"]
    }, 
{
        "scCode": "sccode2",
        "valCodes": ["1ADB"]
    }

]

I believe I could loop through the array and match my keys, but is there a quick way to reformat this without having to explicitly loop through? I've tried using a reduce function below, but it gives undefined errors with find, which i think has something to do with my formatting.

Tried (?) Code

 const resp = data.reduce((acc, ele) => {
          const ant = acc.find(x => x.sccode === ele.sccode);
        }, []);

Yevhen Horbunkov · Accepted Answer · 2020-03-31 19:39:27Z

2

Would this do?

const src = [{"sccode":"sccode1","val":"1ADA"},{"sccode":"sccode2","val":"1ADB"},{"sccode":"sccode1","val":"1ADC"}],

    result = src.reduce((r,{sccode,val}) => {
      const match = r.find(({scCode}) => scCode == sccode)
      match ?
      match.valCodes.push(val) :
      r.push({scCode:sccode, valCodes: [val]})
      return r
    }, [])
    
console.log(result)

.as-console-wrapper{min-height:100%;}

edited Mar 31, 2020 at 19:39

answered Mar 31, 2020 at 19:35

Yevhen Horbunkov

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1 Comment

Evan Bechtol Over a year ago

so fresh and so clean clean

TheGr8_Nik · Accepted Answer · 2020-03-31 20:55:53Z

1

Try the following, I use a map to store a partial state to improve performances preventing to search sccode in an array for every initial object.

let partial = [{
  "sccode": "sccode1",
  "val": "1ADA"
}, {
  "sccode": "sccode2",
  "val": "1ADB"
}, {
  "sccode": "sccode1",
  "val": "1ADC"
}].reduce((map, obj) => {
  if (!map[obj.sccode]) {
    map[obj.sccode] = [obj.val];
  } else {
    map[obj.sccode].push(obj.val);
  }
  return map;
}, {})

Object.keys(partial).map(sccode => ({
  sccode, valCodes: partial[sccode]
}));

edited Mar 31, 2020 at 20:55

answered Mar 31, 2020 at 19:47

TheGr8_Nik

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5 Comments

Yevhen Horbunkov Over a year ago

Even though I agree that, in general, O(n) -time algorithms (your solution) are naturally faster than O(n²) (mine). But it is still questionable at which point (source array size and group key sccode variation) more optimal algorithm will outperform heavier (involving type switching and Object.keys() extraction) implementation.

Yevhen Horbunkov Over a year ago

Unfortunatelly, I couldn't benchmark that as your code fails with error even when copy pasted as is into the console.

TheGr8_Nik Over a year ago

@YevgenGorbunkov look at this stackoverflow.com/questions/17295056/…

Yevhen Horbunkov Over a year ago

as being said, I have no doubts that 2 passes over the array theoretically are faster than single pass with nested look ups (and I don't need to scroll the thread 10 miles long to get convinced). However, it depends on source data structure and typical size whether you will see the performance gain that outweighs slow Object.keyss() mapping and data types switching (not to mention greater code verbosity). If you would manage to post working code at the very beginning I would do my benchmarking and, furthermore, gladly upvoted your answer if it is really blazing fast.

TheGr8_Nik Over a year ago

@YevgenGorbunkov I agree with you, it depends on how much data has to be processed and how many different sccodes there are. Code is working, was missing the return in reduce function.

Nonik · Accepted Answer · 2020-03-31 19:41:37Z

0

try loaddash/groupby

let groupByResult = groupBy(data, function (n) {
          return n.sccode
        });

answered Mar 31, 2020 at 19:41

Nonik

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Comments

Leonardo Oliveira · Accepted Answer · 2020-03-31 19:41:38Z

0

Check this code:

    array.reduce(function(res, value){
        if(!res[value.sccode]) {
            res[value.sccode] = value; 
            res[value.sccode]['valCodes'] = []
            result.push(res[value.sccode]);
        }
        res[value.sccode]['valCodes'].push(value.val); 
        return res; 
    } ,{});

I tested here and it works fine!

answered Mar 31, 2020 at 19:41

Leonardo Oliveira

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1 Comment

Yevhen Horbunkov Over a year ago

Except for it fails with an error ``result` is not defined' and returns an object whereas array is required

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