I have a document structure like this:
{
readings: [
{ t: 'temperature', r: 130 },
{ t: 'humidity', r: 100 }
],
created_at: '2021-01-05T10:28:49.070Z'
},
{
readings: [
{ t: 'temperature', r: 123 },
{ t: 'humidity', r: 456 }
],
created_at: '2021-01-05T10:32:50.727Z'
}
I need to aggregate the documents for a particular reading type.
For example, the result of aggregation for reading type with temperature should be like following:
[
[130, '2021-01-05T10:28:49.070Z'],
[123, '2021-01-05T10:32:50.727Z']
]
How can I do this with an aggregation pipeline or something?
You can't output an array of arrays from an aggregate pipe. But you can output an object with a single array field. Ie:
[
{data: [130, '2021-01-05T10:28:49.070Z']},
{data: [123, '2021-01-05T10:32:50.727Z']}
]
Here's a pipe that does just that https://mongoplayground.net/p/7UPyUICOncq
let result = await collection.aggregate([
{$unwind: '$readings'},
{$match: {
'readings.t': 'temperature'
}},
{"$project": {
_id: 0,
data: ['$readings.r', '$created_at']
}}
])
Then to reach your desired format just map the output
let formattedResult = result.map(({data}) => data)