使用ramda过滤掉唯一的嵌套值

Question

I have a collection of UNIX timestamps that looks like this:

[
  {"start_time":1540458000000, "end_time":1540472400000}, 
  {"start_time":1540458000000, "end_time":1540486800000}, 
  {"start_time":1540458000000, "end_time":1540501200000}, 
  {"start_time":1540472400000, "end_time":1540486800000}, 
  {"start_time":1540472400000, "end_time":1540501200000}, 
  {"start_time":1540486800000, "end_time":1540501200000}
]

I'd like to pick out all the unique values from both start_time and end_time , so I'm left with:

[
  {"start_time":1540458000000}, 
  {"start_time":1540472400000}, 
  {"start_time":1540486800000}
  {"end_time":1540472400000},
  {"end_time":1540486800000}, 
  {"end_time":1540501200000}, 
]

I've looked at using something similar using groupBy , pluck , zipObj and more using the answer here . But with no luck unfortunately.

A nice-to-have would be a ramda function that worked without having to be given specific keys.

Answer 1

Another Ramda approach:

 const {pipe, map, toPairs, unnest, groupBy, head, uniqBy, last, values, apply, objOf} = R const uniqTimes = pipe( map(toPairs), //=> [[['start', 1], ['end', 2]], [['start', 1], ['end', 3]], ...] unnest, //=> [['start', 1], ['end', 2], ['start', 1], ['end', 3], ...] groupBy(head), //=> {start: [['start', 1], ['start', 1], ['start', 4], ...], end: [['end', 2], ...]} map(uniqBy(last)), //=> {start: [['start', 1], ['start', 4], ...], end: [['end', 2], ...]} values, //=> [[['start', 1], ['start', 4], ...], [['end', 2], ...]] unnest, //=> [['start', 1], ['start', 4], ..., ['end', 2], ...] map(apply(objOf)) //=> [{"start": 1}, {"start": 4}, ..., {"end": 2}, ...] ) const timestamps = [{"start_time":1540458000000,"end_time":1540472400000},{"start_time":1540458000000,"end_time":1540486800000},{"start_time":1540458000000,"end_time":1540501200000},{"start_time":1540472400000,"end_time":1540486800000},{"start_time":1540472400000,"end_time":1540501200000},{"start_time":1540486800000,"end_time":1540501200000}] console.log(uniqTimes(timestamps)) 

 <script src="//cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.js"></script> 

This is how I like to use Ramda: build a pipeline of functions that each do simple transformations.

---

Update

A comment asked how to generate an output more like

{
   "start_time": [1540458000000, 1540458000000],
   "end_time": [1540472400000, 1540486800000]
}

This should do that for the same input:

const uniqTimes = pipe(
  map(toPairs), 
  unnest,
  groupBy(head),
  map(map(last)),
  map(uniq)
)

Answer 2

Not sure about ramda, but below plain js function will do that

 const arr = [ {"start_time":1540458000000, "end_time":1540472400000}, {"start_time":1540458000000, "end_time":1540486800000}, {"start_time":1540458000000, "end_time":1540501200000}, {"start_time":1540472400000, "end_time":1540486800000}, {"start_time":1540472400000, "end_time":1540501200000}, {"start_time":1540486800000, "end_time":1540501200000} ]; function foo(arr) { return [...arr.reduce((a, b) => { Object.entries(b).forEach(e => a.set(String(e), e)); return a; }, new Map())].map(([_,e]) => ({ [e[0]]: e[1] })) } console.log(foo(arr)); 

Answer 3

If the properties you want are unknown, but appear in all objects, you can convert each object to pairs, transpose the resulting array, get the unique values of each array, unnest them to a single array, and then convert back to objects:

 const { pipe, map, toPairs, transpose, uniqBy, last, unnest, objOf, apply } = R; const data = [ {"start_time":1540458000000, "end_time":1540472400000}, {"start_time":1540458000000, "end_time":1540486800000}, {"start_time":1540458000000, "end_time":1540501200000}, {"start_time":1540472400000, "end_time":1540486800000}, {"start_time":1540472400000, "end_time":1540501200000}, {"start_time":1540486800000, "end_time":1540501200000} ]; const getUniqueProps = pipe( map(toPairs), transpose, map(uniqBy(last)), unnest, map(apply(objOf)) ); console.log(getUniqueProps(data)); 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.min.js"></script> 

If you know the properties you want, you can groupBy a property, get the first object from each group, and then pick the property you want from each object:

 const { groupBy, prop, concat, pipe, map, head, pick, values } = R; const data = [ {"start_time":1540458000000, "end_time":1540472400000}, {"start_time":1540458000000, "end_time":1540486800000}, {"start_time":1540458000000, "end_time":1540501200000}, {"start_time":1540472400000, "end_time":1540486800000}, {"start_time":1540472400000, "end_time":1540501200000}, {"start_time":1540486800000, "end_time":1540501200000} ]; const getUniqueProp = (propName) => pipe( groupBy(prop(propName)), map(pipe(head, pick([propName]))), values, ); const getStartEnd = (data) => concat( getUniqueProp('start_time')(data), getUniqueProp('end_time')(data), ); console.log(getStartEnd(data)); 

 <script src="https://cdnjs.cloudflare.com/ajax/libs/ramda/0.25.0/ramda.min.js"></script>