[{"companyId":1,"dataFields":{"ghg_emissions_scope1":{"dataField":"ghg_emissions_scope1","iterations":[{"year":"2019","scope1":"12459"},{"year":"2020","scope1":"15483"},{"year":"2021","scope1":"90051"}]},"ghg_emissions_scope2":{"dataField":"ghg_emissions_scope2","iterations":[{"year":"2017","scope2_location_based":"1234","scope2_market_based":"1234"},{"year":"2018","scope2_location_based":"13423","scope2_market_based":"543654"},{"year":"2019","scope2_location_based":"235434","scope2_market_based":"42343"},{"year":"2020","scope2_location_based":"12432334","scope2_market_based":"234423"}]},"ghg_emissions_scope3":{"dataField":"ghg_emissions_scope3","iterations":[{"year":"2018","ghg_emission_associated":"354","ghg_emission_other":"423423","ghg_emissions_products":"967"},{"year":"2019","ghg_emission_associated":"12459","ghg_emission_other":"6545476","ghg_emissions_products":"445663"},{"year":"2020","ghg_emission_associated":"6454","ghg_emission_other":"423432","ghg_emissions_products":"756657"},{"year":"2021","ghg_emission_associated":"234","ghg_emission_other":"1235","ghg_emissions_products":"564"},{"year":"2022","ghg_emission_associated":"4523","ghg_emission_other":"435","ghg_emissions_products":"5345"}]}}}]

db.collection.aggregate([{$addFields:{iterations:{$setUnion:["$dataFields.ghg_emissions_scope1.iterations.year","$dataFields.ghg_emissions_scope2.iterations.year","$dataFields.ghg_emissions_scope3.iterations.year"]}}},{$set:{iterations:{$map:{input:"$iterations",in:{year:"$$this",indexA:{"$indexOfArray":["$dataFields.ghg_emissions_scope1.iterations.year","$$this"]},indexB:{"$indexOfArray":["$dataFields.ghg_emissions_scope2.iterations.year","$$this"]},indexC:{"$indexOfArray":["$dataFields.ghg_emissions_scope3.iterations.year","$$this"]},}}}}},{$project:{companyId:1,data:{$map:{input:"$iterations",in:{$mergeObjects:[{"ghg_emission_associated":null,"ghg_emission_other":null,"ghg_emissions_products":null,"scope1":null,"scope2_location_based":null,"scope2_market_based":null,"year":null},{$cond:[{$gte:["$$this.indexA",0]},{$arrayElemAt:["$dataFields.ghg_emissions_scope1.iterations","$$this.indexA"]},{}]},{$cond:[{$gte:["$$this.indexB",0]},{$arrayElemAt:["$dataFields.ghg_emissions_scope2.iterations","$$this.indexB"]},{}]},{$cond:[{$gte:["$$this.indexC",0]},{$arrayElemAt:["$dataFields.ghg_emissions_scope3.iterations","$$this.indexC"]},{}]}]}}}}},{$project:{companyId:1,year:{$arrayToObject:{$map:{input:"$data",in:{k:"$$this.year",v:"$$this"}}}}}}])