MongoDB $push operator and count characters in a name - mongodb

Question

I've populated a database in Mongodb with the following data in a collection named people.
{ "_id" : 0, "name" : "Bernice Pope", "age" : 69, "date" : "2017-10-04T18:35:44.011Z" }
{ "_id" : 1, "name" : "Eric Malone", "age" : 57, "date" : "2017-10-04T18:35:44.014Z" }
{ "_id" : 2, "name" : "Blanche Miller", "age" : 35, "date" : "2017-10-4T18:35:44.015Z" }
{ "_id" : 3, "name" : "Sue Perez", "age" : 64, "date" : "2017-10-04T18:35:44.016Z" }
{ "_id" : 4, "name" : "Ryan White", "age" : 39, "date" : "2017-10-04T18:35:44.019Z"}
{ "_id" : 5, "name" : "Grace Payne", "age" : 56, "date" : "2017-10-04T18:35:44.020Z" }
{ "_id" : 6, "name" : "Jessie Yates", "age" : 53, "date" : "2017-10-04T18:35:44.020Z"}
{ "_id" : 7, "name" : "Herbert Mason", "age" : 37, "date" : "2017-10-4T18:35:44.020Z" }
{ "_id" : 8, "name" : "Jesse Jordan", "age" : 47, "date" : "2017-10-04T18:35:44.020Z"}
{ "_id" : 9, "name" : "Hulda Fuller", "age" : 25, "date" : "2017-10-04T18:35:44.020Z"}
Based on the people collection, I need to create a view named PeopleNames which likes below:
{ "LengthOfName": 8, "names" : [ "Sue Perez" ]}
{ "LengthOfName" : 9, "names" : [ "Ryan White" ]}
{ "LengthOfName" : 10, "names" : [ "Eric Malone", "Grace Payne" ]}
{ "LengthOfName" : 11, "names" : [ "Bernice Pope", "Jessie Yates", "Jesse Jordan", "Hulda Fuller" ]}
{ "LengthOfName" : 12, "names" : [ "Herbert Mason" ]}
{ "LengthOfName" : 13, "names" : [ "Blanche Miller"]}
LengthOfName is the total number of the characters in the last name and first name.
My approach is to first add the names into an array, the use $split operator to split the names and use $strLenCP to count the characters.
db.people.aggregate([
{
$project : {
name : 1,
name_array : [{$push : { $split : {$name : " "}}}]
}
}
,{
$unwind : "$name_array"
},{
$project : {
name : 1,
nameLength : {$strLenCP : $name_array}
}
},{
$group :{
_id : "$nameLength",
nameLength: 1
}
}])
But I am receiving error saying that my "$name_array" is undefined Any ideas?

Answer 1

The $push aggregation operator is only available in the $group stage.
You can group the documents by the name length (after trimming the spaces in the name using $replaceAll) and use $push to add the names to the names array. You can then add a $project stage to add the LengthOfName field to the documents and finally add a $sort stage to sort the documents by the LengthOfName field.
db.collection.aggregate([
{
$group: {
_id: {
$strLenCP: {
$replaceAll: {
input: "$name",
find: " ",
replacement: ""
}
}
},
names: {
$push: "$name"
}
}
},
{
$project: {
_id: 0,
LengthOfName: "$_id",
names: "$names",
}
},
{
$sort: {
LengthOfName: 1,
}
}
])
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