mongodb - Select array inner element -
i have trouble mongodb data below. want data [projects][log][subject]. so, tried this
$project':{_id:0, projects.log.subject:1} but not correct syntax..
{ "_id": objectid("569f3a3e9d2540764d8bde59"), "a": "book", "server": "us", "projects": [ { "domainarray": [ { ~~~~ } ], "log": [ { ~~~~~, "subject": "i want this" } ], "before": "234234234" }, { "domainarray": [ { ~~~~ } ], "log": [ { ~~~~~, "subject": "i want this" } ], "before": "234234234" },.... ] //end of projects }//end of document how can data group [subject]? have no idea this..
edited- expected data this
{ "subject":"first", "subject":"second", "subject":"third", "subject":"~~~" } is possible? want array of subject.
not sure whether expected result or not. can please try this:
db.project.aggregate([ {$project:{projects:1,_id:0}}, {$unwind:"$projects"}, {$unwind:"$projects.log"}, {$project:{subject:"$projects.log.subject",_id:0}} ]) and map-reduce above result of word count below:
//map function var map = function() { for(var in this.projects) { for(var j in this.projects[i].log) { var arraywords = this.projects[i].log[j].subject.split(" "); for(var k = 0; k < arraywords.length; k++) { emit(arraywords[k],{occurance:1}); } } } }; //reduce function function reduce(word, arrayoccurance) { var totaloccurance = 0; (var = 0; < arrayoccurance.length; i++) { totaloccurance = totaloccurance + arrayoccurance[i].occurance; } return { occurance:totaloccurance }; } //combine both function operation , output result wordoccurance collection db.project.mapreduce( map, reduce, { query: {"projects.log.subject":"~~~~~"}, out: "wordoccurance" } ) //query result output db.wordoccurance.find() you can change query under mapreduce match subject want word count. please let me know if mapreduce function doesn't meet expected result.
you can refer below 2 pages create , troubleshoot map , reduce function:
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