How to Create Nested Group By in UnderScore.js

Question

I have an array I need to group them based on size_y;

[
    {"col":4,"row":1,"size_x":1,"size_y":4}, 
    {"col":2,"row":2,"size_x":1,"size_y":2}, 
    {"col":1,"row":1,"size_x":3,"size_y":1},
    {"col":1,"row":4,"size_x":3,"size_y":1}, 
    {"col":1,"row":5,"size_x":4,"size_y":1}
]

Now, if size_y is 4 I want to group all the rows less than or equal to 4.

[
    {"col":4,"row":1,"size_x":1,"size_y":4}, 
    {"col":2,"row":2,"size_x":1,"size_y":2}, 
    {"col":1,"row":1,"size_x":3,"size_y":1},
    {"col":1,"row":4,"size_x":3,"size_y":1},
],
[
    {"col":1,"row":5,"size_x":4,"size_y":1}
]

thanks in advance.

So you want to get top data structure, from the bottom one? And bottom one is nested array? Is underscore a must? — Georgy
– Georgy, Commented Feb 3, 2019 at 4:05
no, from top data structure I need to get the bottom one. Underscore is recommended but not necessary. — Sravan Sriram
– Sravan Sriram, Commented Feb 3, 2019 at 4:08
What is the data structure at the updated question based on? All of the objects in the array have a "size_y" property, which "size_y" value should be evaluated? — guest271314
– guest271314, Commented Feb 3, 2019 at 4:16
initially, the 1st item should be checked. next, if the "size_y" is more then one then that should create another array as shown in the example. in the second step if the "size_y" is 2 and "row" is 2 then the nested array should contain the elements of row 2,3 only — Sravan Sriram
– Sravan Sriram, Commented Feb 3, 2019 at 4:20
@SravanSriram "initially, the 1st item should be checked." Ok. "next if the "size_y" is more then one then that should create another array as shown in the example." The element adjacent to the fist element has a "size_y" value less than the first element, which is not reflected in the resulting data structure at the updated question, correct?. — guest271314
– guest271314, Commented Feb 3, 2019 at 4:22

guest271314 · Accepted Answer · 2019-02-03 04:25:22Z

2

You can use a generator function and .splice()

let arr = [
    {"col":4,"row":1,"size_x":1,"size_y":4}, 
    {"col":2,"row":2,"size_x":1,"size_y":2}, 
    {"col":1,"row":1,"size_x":3,"size_y":1},
    {"col":1,"row":4,"size_x":3,"size_y":1}, 
    {"col":1,"row":5,"size_x":4,"size_y":1}
];

function* divideBy(a) {
  const [copy, [{size_y}] = copy] = [[...a]];
  while (copy.length) yield copy.splice(0, size_y);
}

let res = [...divideBy(arr)];

console.log(res)

edited Feb 3, 2019 at 4:25

answered Feb 3, 2019 at 4:09

guest271314

1

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2 Comments

Sravan Sriram Over a year ago

size_y this will not be always same.

guest271314 Over a year ago

@SravanSriram The generator function accepts n as second parameter, where n is a positive integer

Code Maniac · Accepted Answer · 2019-02-03 04:07:40Z

1

Using pure JS you can simply do using reduce

let arr = [{"col":4,"row":1,"size_x":1,"size_y":4},{"col":2,"row":2,"size_x":1,"size_y":2},{"col":1,"row":1,"size_x":3,"size_y":1}, {"col":1,"row":4,"size_x":3,"size_y":1},{"col":1,"row":5,"size_x":4,"size_y":1}]

let op = arr.reduce((out,inp)=>{
  if(inp.row > 4){
    if(out['>4']){
      out['>4'].push(inp)
    } else {
      out['>4'] = [inp]
    }
  }else{
    if(out['<4']){
      out['<4'].push(inp)
    } else {
      out['<4'] = [inp]
    }
  }
  return out
},{})

console.log(Object.values(op))

answered Feb 3, 2019 at 4:07

Code Maniac

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1 Comment

Sravan Sriram Over a year ago

size_y this will not be always same

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