PHP MongoDB SUM all columns - php

Question

Is there anyway in which MongoDB aggregate framework can be used to sum up all the columns or an array of columns rather than just one?
Each row has a 'category id'. I'm hoping to filter by a specific category id and then output a row which is the sum of each of the columns. As I wont be needing all of the columns, it would be better if I could specify columns to increase performance.
I have seen examples of this done with 1 column however not with multiple columns.
Below is example data
{ "type" : "A", "a" : 1, "b" : 2, "c" : 3, "d" : 4 }
{ "type" : "A", "a" : 10, "b" : 20, "c" : 30, "d" : 40 }
{ "type" : "B", "a" : 1, "b" : 2, "c" : 3, "d" : 4 }
{ "type" : "B", "a" : 10, "b" : 20, "c" : 30, "d" : 40 }
The result therefore when the type is B would be
{ "type" : "B", "a" : 11, "b" : 22, "c" : 33, "d" : 44 }
As can be seen, each of the columns have been summed up, and a single row is returned with the sum of each column.
I am using PHP and the latest version of MongoDB with Debian
Thanks

Answer 1

We don't have your data for a clear example, but you seem to be basically looking for the $add operator which "add" a list of supplied values together. So given a sample of documents:
{ "type" : "A", "a" : 1, "b" : 2, "c" : 3, "d" : 4 }
{ "type" : "A", "a" : 10, "b" : 20, "c" : 30, "d" : 40 }
{ "type" : "B", "a" : 1, "b" : 2, "c" : 3, "d" : 4 }
{ "type" : "B", "a" : 10, "b" : 20, "c" : 30, "d" : 40 }
There is this example to "add" all the "columns" together for "a", "b" and "c" only. Also grouping by "type":
db.collection.aggregate([
{ "$group": {
"_id": "$type",
"total": { "$sum": { "$add": [ "$a", "$b", "$c" ] } }
}}
])
You can also use $add with $project if you do not need to $group or are otherwise working with data at a different level.
The result on this data would be:
{ "_id" : "B", "total" : 66 }
{ "_id" : "A", "total" : 66 }
What you are actually asking though is just doing a $sum for each column:
db.collection.aggregate([
{ "$group": {
"_id": "$type",
"a": { "$sum": "$a" },
"b": { "$sum": "$b" },
"c": { "$sum": "$c" },
"d": { "$sum": "$d" }
}}
])
Which produces:
{ "_id" : "B", "a" : 11, "b" : 22, "c" : 33, "d" : 44 }
{ "_id" : "A", "a" : 11, "b" : 22, "c" : 33, "d" : 44 }