[{"name":"VAS LAYER BREEDER FARM PRIVATE LIMITED"},{"name":"UTTARA BROILER BREEDER FARM PRIVATE LIMITED"},{"name":"SAI REKHA POULTRY FARMS PRIVATE LIMITED"},{"name":"RUMITECH NUTRITION PRIVATE LIMITED"},{"name":"SARKAR BROILER & AGRO FARMS PRIVATE LIMITED"},{"name":"SAKAR POULTRY PRIVATE LIMITED"}]

db.collection.aggregate([{$project:{name:{$let:{vars:{first:{$arrayElemAt:[{$split:["$name"," "]},0]}},in:{$cond:[{$lte:[{$strLenCP:"$$first"},3]},"$$first",""]}}}}},{$match:{name:{$ne:""}}},{$group:{_id:null,name:{$push:"$name"}}}])