group base on array element mongoDB

Question

Explanation: how we can do the group based on array elements, I want to do a group based on 0 element of both arrays.

{ "st": [ [ "2011-01-04T12:18:41Z", 0 ], [ "2011-01-04T15:00:00Z", 0 ] ], "en": [ [ "2011-01-04T14:59:50Z", 1 ], [ "2011-01-04T15:05:00Z", 4 ] ] }

The expected output document looks like. for example

[ { "st": "2011-01-04T12:18:41Z", "en": "2011-01-04T14:59:50Z", "st_val": 0, "en_val": 1, "total_index_count": 2 }, { "st": "2011-01-04T15:00:00Z", "en": "2011-01-04T15:05:00Z", "st_val": 0, "en_val": 4, "total_index_count": 2 } ]

can you add another more complex example? i'm not sure i understand. do you want to just match index i in st with index i in en arrays? — Tom Slabbaert
– Tom Slabbaert, Commented Sep 13, 2021 at 11:50

Tom Slabbaert · Accepted Answer · 2021-09-13 12:03:29Z

1

You can do this in several different ways, here is an approach utilizing the $map and $arrayElemAt operators.

db.collection.aggregate([ { "$project": { elements: { $map: { input: { $range: [ 0, { $size: "$st" } ] }, in: { st_val: { "$arrayElemAt": [ { "$arrayElemAt": [ "$st", "$$this" ] }, 0 ] }, st: { "$arrayElemAt": [ { "$arrayElemAt": [ "$st", "$$this" ] }, 1 ] }, en_val: { "$arrayElemAt": [ { "$arrayElemAt": [ "$en", "$$this" ] }, 0 ] }, en: { "$arrayElemAt": [ { "$arrayElemAt": [ "$en", "$$this" ] }, 1 ] }, } } } } }, { $unwind: "$elements" }, { $replaceRoot: { newRoot: "$elements" } } ])

Mongo Playground

answered Sep 13, 2021 at 12:03

Tom Slabbaert

22.5k10 gold badges34 silver badges45 bronze badges

Sign up to request clarification or add additional context in comments.

7 Comments

bc110402922 Over a year ago

Its look fine, I have 2 questions. 1. in the project stage how we can count the index of the array total_index_count is missing. 2. In ` "$range":[0,{ "$size": "$st"}] ` why you took st why not en

Tom Slabbaert Over a year ago

the assumption is they are both the same length, if not you should specify the behavior your expecting.

Tom Slabbaert Over a year ago

and i wasn't sure what total_index_count is because they are both 2 in the result you specified.

bc110402922 Over a year ago

st and en both index always be equal. for example, if st has 2 indexes, en should be 2 indexes, so how we can count the index at the project stage is it then we need the group stage?

Tom Slabbaert Over a year ago

mongoplayground.net/p/EP-DQbI9_Kd, like so?

|

Collectives™ on Stack Overflow

group base on array element mongoDB

1 Answer 1

7 Comments

Linked

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

7 Comments

Linked

Related