How do I turn a categorical value into column name

Question

I am new at Javascript, and I am having problems with a list of dictionaries. I have an object such as this one:

0:{Year: "2007", expenditure: "314,448.7", category: "Exports"}
1:{Year: "2008", expenditure: "320,805.2", category: "Exports"}
2:{Year: "2007", expenditure: "314,448.7", category: "Imports"}
3:{Year: "2008", expenditure: "320,805.2", category: "Imports"}

and I would like to turn it into a new one with the values Exports and Imports as two different columns, with its correspondent expenditure below. Something like this:

0:{Year: "2007", Exports: "314,448.7"}
1:{Year: "2008", Exports: "320,805.2"}
2:{Year: "2007", Imports: "314,448.7"}
3:{Year: "2008", Imports: "320,805.2"}

Does anyone know how to do this? Thank you in advance.

FYI In JavaScript these are not dictionaries, they're Objects — zfrisch, Apr 13 '18 at 19:58
@barmar today you are closing everything. The dupe seems to be just slightly related. — Jonas Wilms, Apr 13 '18 at 20:00
@JonasW. Unless he doesn't know how to loop over an array, what other problem could he have than creating a new object with a dynamic property name? — Barmar, Apr 13 '18 at 20:02
Sorry, I made a mistake in my question. What I would like to get is something like this: 0:{Year: "2007", Exports: "314,448.7", Imports: "314,448.7"} 1:{Year: "2008", Exports: "320,805.2", Imports: "320,805.2"} — Michael Ro, Apr 14 '18 at 09:22

score 0 · Answer 1 · answered Apr 13 '18 at 19:57

0

This would be a good job for reduce:

let arry = [{
    Year: "2007",
    expenditure: "314,448.7",
    category: "Exports"
  },
  {
    Year: "2008",
    expenditure: "320,805.2",
    category: "Exports"
  },
  {
    Year: "2007",
    expenditure: "314,448.7",
    category: "Imports"
  },
  {
    Year: "2008",
    expenditure: "320,805.2",
    category: "Imports"
  }
]

let result = arry.reduce((r, v) => r.concat([{
  Year: v.Year,
  [v.category]: v.expenditure
}]), [])

console.log(result)

answered Apr 13 '18 at 19:57

Get Off My Lawn

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Wouldn't `map` be even easier? – Barmar Apr 13 '18 at 19:59
Yes, I didn't realize that it returned a new array. For some reason I thought it modified the array in place. – Get Off My Lawn Apr 13 '18 at 20:00

Jonas Wilms · Answer 2 · 2018-04-13T19:59:53.263

0

    const output = input.map(({Year, expenditure, category}) => ({Year, [category]: expenditure }));

Just destructure every object and build up a new one. You can also include all other propertues in the new object using rest/spread:

 const output = input.map(({expenditure, category, ...rest}) => ({[category]: expenditure, ...rest }));

edited Apr 13 '18 at 19:59

answered Apr 13 '18 at 19:58

Jonas Wilms

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1

@GetOffMyLawn map returns a new array, and the OP asked to transform the current array into the two key one. – zfrisch Apr 13 '18 at 19:59

How do I turn a categorical value into column name

2 Answers2