Combine object with key values matching to pattern

I am trying to split the object based on the keys starting with a pattern like S.1.1.0.

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const obj = {
  "S.1.1.0": "Hi",
  "S.1.1.1": "what is your name",
  "S.1.1.2": "Can we meet",
  "S.2.1.1": "what is the time now",
  "S.2.1.2a": "It is 6 PM",
  "S.3.1.1b": "where do you live",
  "S.3.1.2": "how is the weather",
  "S.3.1.3": "it is very cold",
  "S.3.1.3b": "yes",
}

const result = Object.entries(obj).reduce((a, [key, val]) => { 
  const [s, k, v] = key.split('.')  
  const item = a.find(({
    key: itemkey
  }) => itemkey === k)  
 console.log(item)
  if (item) {  
    item[v] = val
  } else {  
    a.push({
      key: k,
      [v]: val
    })
  }

  return a
}, [])

console.log(result)

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Expecting the output to be like where key value starting with S.1 combined together. The key value is dynamic by always starts like S.1, S.2 ...

 [{
        "S.1.1.0": "Hi",
        "S.1.1.1": "what is your name",
        "S.1.1.2": "Can we meet"
      },
      {
        "S.2.1.1": "what is the time now",
        "S.2.1.2a": "It is 6 PM"
      },
      {
        "S.3.1.1b": "where do you live",
        "S.3.1.2": "how is the weather",
        "S.3.1.3": "it is very cold",
        "S.3.1.3b": "yes"
      }
    ]

You could reduce() to an object with the mapping key as index.

Then use Object.values(result) to get the desired result

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const obj = {
  "S.1.1.0": "Hi",
  "S.1.1.1": "what is your name",
  "S.1.1.2": "Can we meet",
  "S.2.1.1": "what is the time now",
  "S.2.1.2a": "It is 6 PM",
  "S.3.1.1b": "where do you live",
  "S.3.1.2": "how is the weather",
  "S.3.1.3": "it is very cold",
  "S.3.1.3b": "yes",
}

const result = Object.entries(obj).reduce((a, [key, val]) => { 
  const mapping = key.split('.', 2).join('.');
  
  if (!a[mapping]) a[mapping] = { };
  a[mapping][key] = val;
  
  return a;
}, {})

const resultArray = Object.values(result);

console.log(resultArray)

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Output:

[
  {
    "S.1.1.0": "Hi",
    "S.1.1.1": "what is your name",
    "S.1.1.2": "Can we meet"
  },
  {
    "S.2.1.1": "what is the time now",
    "S.2.1.2a": "It is 6 PM"
  },
  {
    "S.3.1.1b": "where do you live",
    "S.3.1.2": "how is the weather",
    "S.3.1.3": "it is very cold",
    "S.3.1.3b": "yes"
  }
]

If you want to be efficient, you can build a Map and bin each key-value pair by criteria specified by the keyFn.

const keyFn = (prop) => prop.match(/(?<=S\.)\d+/)[0]

Example

Here is the code in action:

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const obj = {
  "S.1.1.0": "Hi",
  "S.1.1.1": "what is your name",
  "S.1.1.2": "Can we meet",
  "S.2.1.1": "what is the time now",
  "S.2.1.2a": "It is 6 PM",
  "S.3.1.1b": "where do you live",
  "S.3.1.2": "how is the weather",
  "S.3.1.3": "it is very cold",
  "S.3.1.3b": "yes",
}

const groupBy = (obj, keyFn) =>
  [...Object
    .entries(obj)
    .reduce((map, [prop, value]) => {
        const key = keyFn(prop), entries = map.get(key) ?? [];
        entries.push([prop, value]);
        return map.set(key, entries);
      }, new Map)
    .values()]
    .map(entries => Object.fromEntries(entries))

const grouped = groupBy(obj, (prop) => prop.match(/(?<=S\.)\d+/)[0]);

console.log(grouped);

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Here is the same, but it uses lodash. I created a mixin that takes an object and a key pattern.

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const obj = {
  "S.1.1.0": "Hi",
  "S.1.1.1": "what is your name",
  "S.1.1.2": "Can we meet",
  "S.2.1.1": "what is the time now",
  "S.2.1.2a": "It is 6 PM",
  "S.3.1.1b": "where do you live",
  "S.3.1.2": "how is the weather",
  "S.3.1.3": "it is very cold",
  "S.3.1.3b": "yes",
}

_.mixin({
  groupByPattern : (object, keyPattern) =>
    _.chain(obj)
      .entries()
      .groupBy(([prop, value]) => prop.match(keyPattern)?.[0])
      .values()
      .map(_.fromPairs)
      .value()
});

const grouped = _.groupByPattern(obj, /(?<=S\.)\d+/);

console.log(grouped);

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.as-console-wrapper { top: 0; max-height: 100% !important; }

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<script src="https://cdnjs.cloudflare.com/ajax/libs/lodash.js/4.17.21/lodash.min.js"></script>

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