Count frequency of different key values in Javascript object?-CodePudding

Looking for a very simple, elegant solution to count the frequency of different values in a javascript object. For example:

var input = [
    {"a": "1", "b": "2"},
    {"a": "2", "b": "2"},
    {"a": "2", "b": "2", "c": "2"},
    {"a": "bananas"}
]

var output = {
    "a": {"1": 1, "2": 2, "bananas": 1},
    "b": {"2": 3},
    "c": {"2": 1},
}

I could probably loop over everything manually, but is there a simple and elegant solution, probably using reducers?

CodePudding user response：

you can do something like this

const occurencies = data => data.reduce((res, item) => {
  Object.entries(item).forEach(([k, v]) => {
    const existing = res[k] || {}
    existing[v] = (existing[v] || 0)   1
    res[k] = existing
  })

return res

}, {})


var input = [
    {"a": "1", "b": "2"},
    {"a": "2", "b": "2"},
    {"a": "2", "b": "2", "c": "2"},
    {"a": "bananas"}
]

console.log(occurencies(input))

CodePudding user response：

a reduce and a forEach. Object.entries to get the entries of each element of input array. Nullish coalescing operator(??) to shorten the logic acc[k]=acc[k]||{}

var input = [
    {"a": "1", "b": "2"},
    {"a": "2", "b": "2"},
    {"a": "2", "b": "2", "c": "2"},
    {"a": "bananas"}
]

const output = input.reduce((acc,curr)=>{
  const entries = Object.entries(curr)
  entries.forEach(([k,v])=>{
    acc[k]??={}  //initializing key if not present
    acc[k][v]??=0 //initializing count if not present for each value
    acc[k][v]   //incrementing
    })
   return acc
},{})

console.log(output)