suissa

const group = (obj, field) => obj[field]

const addValue = (result, obj, field) => 
  result[obj[field]] || []

const addToGroup = (result, obj, field) => 
  [...(addValue(result, obj, field)), obj]

const toNewGroupUsing = (field) => (result, obj) => ({
  ...result, 

suissa

const toNewGroup = (field) => (result, obj) => ({
  ...result, 
  [obj[field]]: [...(result[obj[field]] || []), obj]
})

const group = (list) => (field) => 
  list.reduce(toNewGroup(field), {})

const groupBy = group(list)

suissa

const toNewGroup = (field) => (result, obj) => ({
  ...result, 
  [obj[field]]: [...(result[obj[field]] || []), obj]
})

const groupBy = (list, field) => 
  list.reduce(toNewGroup(field), {})

console.log(groupBy(list, "level"))

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const toNewGroup = (field) => (result, obj) => ({
  ...result, 
  [obj[field]]: [...(result[obj[field]] || []), obj]
})

const groups = list.reduce(toNewGroup("level"), {})

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const toNewGroup = (field) => (result, obj) => {
  result[obj[field]] = (!result[obj[field]])
    ? [obj]
    : [...result[obj[field]], obj]
  return result
}

const groups = list.reduce(toNewGroup("level"), {})

console.log(groups)

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const toNewGroup = (field) => (result, obj) => {
  result[field] = (!result[field])
    ? [obj]
    : [...result[field], obj]
  return result
}

const groups = list.reduce(toNewGroup("level"), {})

console.log(groups)

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{ senior: 
  [ { id: 1,
      name: 'Suissa',
      active: true,
      level: 'senior',
      tags: [Array] },
    { id: 2,
      name: 'Bella',
      active: true,
      level: 'senior',

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const plenos = list.filter(toGroup("level", "pleno"))
console.log({plenos})

/**
{ plenos: 
   [ { id: 4,
       name: 'John',
       level: 'pleno',
       active: false,
       tags: [Array] } ] }

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const toGroup = (field, value) => (obj) => 
  obj[field] === value

const filtered = list.filter(toGroup("level", "senior"))

console.log({filtered})
/**
{ filtered: 
   [ { id: 1,
       name: 'Suissa',

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const obj1 = {
  id: 1,
  name: "Suissa",
  active: true,
  level: "senior",
  tags: [
    "teacher",
    "dev",
    "js"
  ]